A comparison of three methods of analysis for age-period-cohort models with application to incidence data on non-Hodgkin's lymphoma

Trends in breast cancer mortality attributable to metabolic risks in Chinese women from 1990 to 2019: an age-period-cohort analysis

Objective

Metabolic risks (MRs) are the primary determinants of breast cancer (BC) mortality among women. This study aimed to examine the changing trends in BC mortality associated with MRs and explore how they related to age, time period, and birth cohorts in Chinese women aged 25 and above.

Methods

Data were sourced from the Global Burden of Disease Study 2019 (GBD2019). The BC mortality trajectories and patterns attributable to MRs were assessed using Joinpoint regression. The age-period-cohort (APC) model was employed to evaluate cohort and time period effects.

Results

The age-standardized mortality rate (ASMR) of BC mortality linked to MRs displayed an escalating trend from 1990 to 2019, demonstrating an average annual percentage change (AAPC) of 1.79% (95% CI: 1.69~1.87). AAPCs attributable to high fasting plasma glucose (HFPG) and high body mass index (HBMI) were 0.41% (95% CI: 0.32~0.53) and 2.75% (95% CI: 2.68~2.82), respectively. APC analysis revealed that BC mortality due to HBMI in women aged 50 and above showed a rise with age and mortality associated with HFPG consistently demonstrated a positive correlation with age. The impact of HBMI on BC mortality significantly outweighed that of HFPG. The risk of BC mortality linked to HBMI has steadily increased since 2005, while HFPG demonstrated a trend of initial increase followed by a decrease in the period effect. Regarding the cohort effect, the relative risk of mortality was greater in the birth cohort of women after the 1960s of MRs on BC mortality, whereas those born after 1980 displayed a slight decline in the relative risk (RR) associated with BC mortality due to HBMI.

Conclusion

This study suggests that middle-aged and elderly women should be considered as a priority population, and control of HBMI and HFPG should be used as a primary tool to control metabolic risk factors and effectively reduce BC mortality.

Temporal trends in lung cancer mortality and years of life lost in Wuhan, China, 2010-2019

Objective

Lung cancer is responsible for millions of deaths yearly, and its burden is severe worldwide. This study aimed to investigate the burden of lung cancer in the population of Wuhan based on the surveillance data from 2010 to 2019.

Methods

Data of this study was obtained from the Mortality Register System established by the Wuhan Center for Disease Control and Prevention. The study systematically analyzed the burden of lung cancer deaths in the population of Wuhan and its 13 administrative regions from 2010 to 2019 via the Joinpoint regression models, Age-Period-Cohort (APC) models, and decomposition analysis.

Results

This study found the upward and downward trends in the age-standardized mortality rates (ASMRs) and age-standardized years of life lost rates (ASYLLRs) of lung cancer from 2010 to 2019. In Joinpoint regression models, the corresponding estimated annual percentage change (EAPC) were 1.00% and -1.90%, 0.60%, and -3.00%, respectively. In APC models, lung cancer mortality tended to increase with age for both sexes in Wuhan, peaking at the 85-89 age group; The period effects for different populations have started to gradually decline in recent years. In addition, the cohort effects indicated that the risk of lung cancer death was highest among those born in the 1950s-1955s, at 1.08 (males) and 1.01 (females). Among all administrative districts in Wuhan, the ASMR of lung cancer in the Xinzhou District has remained the highest over the study period. In decomposition analysis, both population aging (P<0.01) and population growth (P<0.01) aggravated (Z>0) lung cancer deaths in the Wuhan population.

Conclusions

The burden of lung cancer death in the Wuhan population has shown a gradual decline in recent years, but the impact of aging and population growth on lung cancer mortality should not be ignored. Therefore, lung cancer surveillance must be strengthened to reduce the burden of lung cancer in Wuhan.

Incidence and mortality trends of nasopharynx cancer from 1990 to 2019 in China: an age-period-cohort analysis

Background

Nasopharynx cancer (NPC) is a great health burden in China. This study explored the long-term trends of NPC incidence and mortality in China.

Methods

We retrospectively analyzed data from the Global Burden of Disease Study 2019 using an age-period-cohort framework.

Results

The age-standardized incidence rate (ASIR) of NPC increased by 72.7% and age-standardized mortality rate (ASMR) of NPC decreased by 51.7% for both sexes between 1990 and 2019. For males, the local drift for incidence was higher than 0 (P < 0.05) in those aged 20 to 79 years. For females, the local drift was higher than 0 (P < 0.05) in those aged 30 to 59 years, and lower than 0 (P < 0.05) in those aged 65 to 84 years. The local drift for mortality rates were less than 0 (P < 0.05) in every age group for both sexes. The estimated period relative risks (RRs) for incidence of NPC were increased monotonically for males, and increased for females after 2000. The increasing trend of cohort RRs of incidence was ceased in recent birth cohorts. Both period and cohort effects of NPC mortality in China decreased monotonically.

Conclusions

Over the last three decades, the ASMR and crude mortality rate (CMR) of NPC has decreased, but the ASIR and crude incidence rate (CIR) increased in China. Although the potential mortality risk of NPC decreased, the risk of NPC incidence was found to increase as the period move forward, and suggested that control and prevention efforts should be enhanced.

Age-Period-Cohort Analysis of Trends in Mental Health Mortality in India from 2001 to 2015

The current study was done to examine the trend of mental health mortality in India using age-period-cohort (APC) analysis. We have conducted a secondary data analysis by using the data on mental health mortality from WHO Global Health Estimates. We performed APC analysis by weighted least squares regression with assumption that data follows Poisson distribution.Annual increase in the age adjusted mortality rate due to mental health problems was 1.52%. Rate ratio (RR) increased consistently across all the age groups from 15-19 to 80-84 years. RR of period effects also showed increase from 2001-2005 to 2011-2015 periods. RR of cohort effects showed consistent increase from 1921-1925 to 1986-1990 cohorts and then decreasing from 1991-1995 to 1996-2000. To summarize, we found that mental health mortality shows increasing trend in India over the past decade with maximum increase among older population.

Worldwide trends in breast cancer incidence from 1993 to 2012: Age-period-cohort analysis and joinpoint regression

Background:

Breast cancer is the most common cancer accounting for about one-fourth of total cancer cases and 15% of all cancer deaths among women worldwide. It is important to determine its trend across the regions in the world to find the high-focus regions. Hence, the current study was done to assess the global trends and deviations in the incidence of breast cancer.

Materials and Methods:

A descriptive trend analysis was done using the data on breast cancer incidence from the WHO Cancer Incidence Data of Five Continents plus database. Joinpoint regression was performed to determine the average annual percent change (AAPC), and age-period-cohort analysis was done to obtain age-, period-, and cohort-specific deviations and rate ratio.

Results:

All the regions showed an increasing trend in breast cancer incidence, with an exception of America. Maximum increase was observed in Asia (AAPC = 2.6%; 95% confidence interval [CI]: 2.4%–2.9%) followed by Europe (AAPC = 0.7%; 95% CI: 0.5%–1%). There was consistent rise in the breast cancer incidence across the age groups in all the four continents with maximum burden in elderly (P < 0.001). Except in America, all other regions showed consistent rise in the incidence of breast cancer through the periods 1998–2002 to 2007–2012 (P < 0.001). There was consistent increase across the cohorts from 1923–1927 to 1978–1982 in continents such as Asia and Oceania (P < 0.001).

Conclusion:

To summarize, the incidence of breast cancer shows an increasing trend globally with a maximum increase in the Asian region. This makes a strong need for newer strategies irrespective of current prevention and control interventions.

Cancer Mortality in Córdoba, Argentina, 1986–2006: An Age-Period-Cohort Analysis

Aims and background

Cancer is the second main cause of death in Argentina, surpassed only by cardiovascular disease. However, analytical approaches isolating some of the known effects, such as age at death, period of death and birth cohort, have never been performed in cancer mortality studies in Argentina. The aim of this study was to analyze cancer mortality trends in a representative region of the country, the Córdoba province (1986–2006).

Methods and study design

Overall age-standardized (world population) mortality rates for cancer (all sites) were computed by a direct method. Joinpoint regression was fitted to the age-standardized mortality rates for both sexes to provide estimated and 95% confidence intervals of the annual percentage changes. The effects of age (15 age groups), period of death (1986–90, 1991–95, 1996–00 or 2001–06), and birth cohort (18 overlapping 10-year birth cohorts) covariates on mortality rates were estimated using a sequentially fitted Poisson regression model.

Results

During the study period, 102,737 people died of cancer in Córdoba, with the age-standardized mortality rates decreasing from 139.3 to 118.7/100,000 person-years. Although this reduction was more noticeable in men, the joinpoint regression model showed a significant change of the age-standardized mortality rates after 1996 in both sexes. Age-period-cohort analysis suggested that the cancer mortality trends may be linked with a strong age effect and a moderate or mild period and cohort effect, related to sex and place of residence.

Conclusions

Based on the observed cohort effect, it maybe argued that there has been a lower exposure level to some risk factors, such as diet and other environmental factors, in Cordoba over the last decades.

A geographical study of thyroid cancer incidence in north-west England following the Windscale nuclear reactor fire of 1957

The Windscale nuclear reactor fire at Sellafield, United Kingdom, in October 1957 led to an uncontrolled release of iodine-131 (radioactive half-life, 8 d) into the atmosphere. Contamination from the accident was most pronounced in the counties of Cumbria and Lancashire, north-west England. Radioiodine concentrates in the thyroid gland producing an excess risk of thyroid cancer, notably among those exposed as children, which persists into later life. For an initial investigation of thyroid cancer incidence in north-west England, data were obtained on cases of thyroid cancer among people born during 1929-1973 and diagnosed during 1974-2012 while resident in England, together with corresponding populations. Incidence rate ratios (IRRs), with Poisson 95% confidence intervals (CIs), compared thyroid cancer incidence rates in Cumbria and in Lancashire with those in the rest of England. For those aged  <20 years in 1958, a statistically significantly increased IRR was found for those diagnosed during 1974-2012 while living in Cumbria (IRR  =  1.29; 95% CI 1.09-1.52), but the equivalent IRR for Lancashire was marginally non-significantly decreased (IRR  =  0.91; 95% CI 0.80-1.04). This pattern of IRRs was also apparent for earlier births, and the significantly increased IRR in Cumbria extended to individuals born in 1959-1963, who would not have been exposed to iodine-131 from the Windscale accident. Moreover, significant overdispersion was present in the temporal distributions of the IRRs, so that Poisson CIs substantially underestimate statistical uncertainties. Consequently, although further investigations are required to properly understand the unusual patterns of thyroid cancer IRRs in Cumbria and Lancashire, the results of this preliminary study are not consistent with an effect of exposure to iodine-131 from the Windscale accident.

Age-period-cohort analysis of trends in amyotrophic lateral sclerosis incidence

Amyotrophic Lateral Sclerosis (ALS) is a progressive neurodegenerative disease with an unknown cause. Studies have reported that the incidence rate of ALS might be changing. As ALS is an age related disease, crude incidence could increase as population structure changes and overall life expectancy improves. Age-period-cohort (APC) models are frequently used to investigate trends in demographic rates such as incidence. Age-specific incidence rate for ALS from 1996 to 2014 were taken from a population-based ALS register in Ireland. To circumvent the well-known identifiability issue in APC models, we apply the method of Partial Least Squares Regression to separate the effects of Age, Period and Cohort on ALS incidence over time. This APC analysis shows no cohort effect and the initial signs of a period effect; increasing incidence of ALS in the most recently diagnosed group. As further years of data accrue to the Irish register it will become clear if this effect emerges as a strong trend in the incidence of ALS in Ireland and replication of these analyses in other populations will show if our findings on temporal patterns in ALS incidence are shared elsewhere.

Forecasting hepatocellular carcinoma mortality in Taiwan using an age-period-cohort model

Hepatocellular carcinoma (HCC) is a common primary malignancy of the liver. Estimates of the future HCC burden are important for health planning. The authors applied an age-period-cohort (APC) model for a 15-year forecast of HCC mortality in Taiwan (based on mortality data between the years 1976 and 2005). It is found that for men, the mortality trend reverses itself in the period 2011-2015, from an increasing one to a slightly deceasing one. For women, the increasing trend reverses itself in the period 2001-2005. The age-adjusted HCC mortality for men and women in the most recent available years, 2006-2008, both fall in the range forecast by the APC model. Forecasting using the APC model can provide an advanced warning of trend reversals.

Increasing incidence of thyroid cancer in Great Britain, 1976-2005: age-period-cohort analysis

Increases in the incidence of thyroid cancer have been previously reported. The purpose of the present study was to examine temporal trends in the incidence of primary thyroid cancer diagnosed in 0-49 year olds in parts of Great Britain during 1976-2005. Data on 4,337 cases of thyroid cancer were obtained from regional cancer registries. Age-standardized incidence rates (ASRs) were calculated. Negative binomial regression was used to examine effects of age, sex, drift (linear trend), non-linear period and non-linear cohort. The best fitting negative binomial regression model included age (P < 0.001), sex (P < 0.001) and drift (P < 0.001). Non-linear period (P = 0.648) and non-linear cohort (P = 0.788) were not statistically significant. For males aged 0-14, the ASR increased from 0.2 per million persons per year in 1976-1986 to 0.6 in 1997-2005. For males aged 15-29 and 30-49 the ASRs increased from 1.9 to 3.3 and from 7.4 to 12.7, respectively. For females aged 0-14, the corresponding ASR increased from 0.3 to 0.5. For females aged 15-29 and 30-49 the ASRs increased from 6.9 to 12.4 and from 21.2 to 42.3, respectively. For all age groups, there has been a linear increase in incidence of thyroid cancer, which has led to a doubling of the number of cases diagnosed over a twenty year span. The reasons for this increase are not well understood, but it is consistent with findings from other countries.

Age, period and cohort effects on the incidence of motorcyclist casualties in traffic crashes

Objectives

(1) Estimate age, period and cohort effects for motorcyclist traffic casualties 1979–2008 in New Zealand and (2) forecast the incidence of New Zealand motorcycle traffic casualties for the period 2019–2023 assuming future age, cohort and period effects, and compare these with an estimate based on simple linear extrapolation.

Methods

Age-period-cohort (APC) modelling was used to estimate the individual effects of age, period and cohort after adjusting for the other two factors. Forecasting was produced for three period-effect scenarios.

Results

After adjusting for cohort and period effects, 15–19-year-olds have substantially elevated risk. The period effect reduced in significance over time until the last period, 2004–2008, where the risk was higher than the preceding period. The 10-year cohorts born 1949–1958, 1954–1963, 1959–1968 and 1964–1973, had elevated risk. The forecasting, based on APC modelling, resulted in the lowest estimates of the future incidence being approximately one-third that of the highest estimate (6641).

Conclusion

Trends in motorcycle casualties have been influenced by significant independent age, period and cohort effects. These need to be considered in forecasting future casualties. The selection of the period effect has a significant impact on the estimates. Which period-effect scenario readers choose to accept depends on their views about a wide range of factors which might influence motorcycle use and crash risk over time.

Cohort effects explain the increase in autism diagnosis among children born from 1992 to 2003 in California

BACKGROUND

The incidence and prevalence of autism have dramatically increased over the last 20 years. Decomposition of autism incidence rates into age, period and cohort effects disentangle underlying domains of causal factors linked to time trends. We estimate an age-period-cohort effect model for autism diagnostic incidence overall and by level of functioning.

METHODS

Data are drawn from sequential cohorts of all 6 501 262 individuals born in California from 1992 to 2003. Autism diagnoses from 1994 to 2005 were ascertained from the California Department of Development Services Client Development and Evaluation Report.

RESULTS

Compared with those born in 1992, each successively younger cohort has significantly higher odds of an autism diagnosis than the previous cohort, controlling for age and period effects. For example, individuals born in 2003 have 16.6 times the odds of an autism diagnosis compared with those born in 1992 [95% confidence interval (CI) 7.8-35.3]. The cohort effect observed in these data is stronger for high than for low-functioning children with an autism diagnosis.

DISCUSSION

Autism incidence in California exhibits a robust and linear positive cohort effect that is stronger among high-functioning children with an autism diagnosis. This finding indicates that the primary drivers of the increases in autism diagnoses must be factors that: (i) have increased linearly year-to-year; (ii) aggregate in birth cohorts; and (iii) are stronger among children with higher levels of functioning.

Age, period, and cohort analysis of regular dental care behavior and edentulism: a marginal approach

Background

To analyze the regular dental care behavior and prevalence of edentulism in adult Danes, reported in sequential cross-sectional oral health surveys by the application of a marginal approach to consider the possible clustering effect of birth cohorts.

Methods

Data from four sequential cross-sectional surveys of non-institutionalized Danes conducted from 1975-2005 comprising 4330 respondents aged 15+ years in 9 birth cohorts were analyzed. The key study variables were seeking dental care on an annual basis (ADC) and edentulism. For the analysis of ADC, survey year, age, gender, socio-economic status (SES) group, denture-wearing, and school dental care (SDC) during childhood were considered. For the analysis of edentulism, only respondents aged 35+ years were included. Survey year, age, gender, SES group, ADC, and SDC during childhood were considered as the independent factors. To take into account the clustering effect of birth cohorts, marginal logistic regressions with an independent correlation structure in generalized estimating equations (GEE) were carried out, with PROC GENMOD in SAS software.

Results

The overall proportion of people seeking ADC increased from 58.8% in 1975 to 86.7% in 2005, while for respondents aged 35 years or older, the overall prevalence of edentulism (35+ years) decreased from 36.4% in 1975 to 5.0% in 2005. Females, respondents in the higher SES group, in more recent survey years, with no denture, and receiving SDC in all grades during childhood were associated with higher probability of seeking ADC regularly (P < 0.05). The interaction of SDC and age (P < 0.0001) was significant. The probabilities of seeking ADC were even higher among subjects with SDC in all grades and aged 45 years or older. Females, older age group, respondents in earlier survey years, not seeking ADC, lower SES group, and not receiving SDC in all grades were associated with higher probability of being edentulous (P < 0.05).

Conclusions

With the use of GEE, the potential clustering effect of birth cohorts in sequential cross-sectional oral health survey data could be appropriately considered. The success of Danish dental health policy was demonstrated by a continued increase of regular dental visiting habits and tooth retention in adults because school dental care was provided to Danes in their childhood.

Age, cohort and period effects on hip fracture incidence: analysis and predictions from New Zealand data 1974-2007

Hip fractures are substantial problem worldwide. The increase in rate with age does not continue into very old age. Rates decline in successive birth cohorts. If the increasing trend in period effect continues, there will be a substantial increase in hip fracture incidence.

INTRODUCTION

The purpose of this study is to (1) determine incidence rates for fracture neck of femur (FNF) for the period 1974-2007, (2) estimate age, cohort, and period effects, and (3) predict the burden of FNF in 2025.

METHODS

Age adjusted incidence rates were estimated using New Zealand hospital discharge data for 1974-2007. Age-period-cohort modeling was used to estimate individual effects of these factors after adjusting for the other two factors. Future fracture burden was estimated under two scenarios.

RESULTS

Age-adjusted rates for women increased from 1974 to 1987 whereas rates for men have increased from 1974 until 2007. Risk increased from 70 years of age but dropped among the very elderly. Period effects showed a steady increase in risk throughout 1974-2007. In contrast, the risk was lower in later cohorts. If there is no change in the period effect from 2007 we estimate a reduction in the burden of illness from FNF, especially for women. However if the period effect continues to increase, there will be substantial increases in FNF incidence, especially for men.

CONCLUSIONS

The effect of population aging on FNF incidence is predictable because projections are based on an existing population. The increasing health and improvement in measures of physical status of older people through the last century, explain the decline in FNF incidence in later cohorts. The steady increase in period effect may be due to increased survival of the very frail. This burden of illness resulting from FNFs must be addressed by population based, research proven approaches to fall and fracture prevention.

A multiphase method for estimating cohort effects in age-period contingency table data

PURPOSE

Understanding the effects of age, period, and cohort on disease morbidity and mortality may help identify etiological factors and inform prevention programs. We illustrate a three-phase method that conceptualizes the cohort effect as a partial interaction between age and period. As an example of application, we analyze homicide mortality data for males in the United States from 1935 through 2004.

METHODS

The three-phased method begins with graphical inspection; second, a median polish is used to remove the log-additive components of age and period effects; third, a linear regression of residuals from the median polish is modeled to quantify the relative magnitude of the cohort effect.

RESULTS

Individuals born after 1960 have a significantly increased rate of homicide relative to those born between 1920 and 1924. After removal of the log-additive effects of age and period, the estimated homicide rate for men born between 1980 and 1984 is more than twice the rate for men born between 1920 and 1924 (rate ratio, 2.11; 95% confidence interval, 1.98-2.25).

CONCLUSION

The three-phase method presented herein offers several advantages, the foremost being an alternative conceptualization of the cohort effect not as an independent component of age and period effects, but as a partial interaction. In addition, the strengths of the method include computational simplicity, interpretability, and reliability.

Age-period-cohort modelling of non-Hodgkin's lymphoma incidence in a French region: a period effect compatible with an environmental exposure

BACKGROUND

The incidence of non-Hodgkin's lymphoma (NHL) has risen steadily during the last few decades in all geographic regions covered by cancer registration for reasons that remain unknown. The aims of this study were to assess the relative contributions of age, period and cohort effects to NHL incidence patterns and therefore to provide clues to explain the increasing incidence.

METHODS

Population and NHL incidence data were provided for the Doubs region (France) during the 1980-2005 period. NHL counts and person-years were tabulated into one-year classes by age (from 20 to 89) and calendar time period. Age-period-cohort models with parametric smooth functions (natural splines) were fitted to the data by assuming a Poisson distribution for the observed number of NHL cases.

RESULTS

The age-standardised incidence rate increased from 4.7 in 1980 to 11.9 per 100,000 person-years at risk in 1992 (corresponding to a 2.5-fold increase) and stabilised afterwards (11.1 per 100,000 in 2005). Age effects showed a steadily increasing slope up to the age of 80 and levelled off for older ages. Large period curvature effects, both adjusted for cohort effects and non-adjusted (p < 10-4 and p < 10-5, respectively), showed departure from linear periodic trends; period effects jumped markedly in 1983 and stabilised in 1992 after a 2.4-fold increase (compared to the 1980 period). In both the age-period-cohort model and the age-cohort model, cohort curvature effects were not statistically significant (p = 0.46 and p = 0.08, respectively).

CONCLUSIONS

The increased NHL incidence in the Doubs region is mostly dependent on factors associated with age and calendar periods instead of cohorts. We found evidence for a levelling off in both incidence rates and period effects beginning in 1992. It is unlikely that the changes in classification (which occurred after 1995) and the improvements of diagnostic accuracy could largely account for the 1983-1992 period-effect increase, giving way to an increased exposure to widely distributed risk factors including persistent organic pollutants and pesticides. Continued NHL incidence and careful analysis of period effects are of utmost importance to elucidate the enigmatic epidemiology of NHL.

What is a cohort effect? Comparison of three statistical methods for modeling cohort effects in obesity prevalence in the United States, 1971-2006

Analysts often use different conceptual definitions of a cohort effect, and therefore different statistical methods, which lead to differing empirical results. A definition often used in sociology assumes that cohorts have unique characteristics confounded by age and period effects, whereas epidemiologists often conceive that period and age effects interact to produce cohort effects. The present study aims to illustrate these differences by estimating age, period, and cohort (APC) effects on obesity prevalence in the U.S. from 1971 to 2006 using both conceptual approaches. Data were drawn from seven cross-sectional waves of the National Health and Nutrition Examination Survey. Obesity was defined as BMI >or=30 for adults and >or=95th percentile for children under the age of 20. APC effects were estimated using the classic constraint-based method (first-order effects estimated and interpreted), the Holford method (first-order effects estimated but second-order effects interpreted), and median polish method (second-order effects are estimated and interpreted). Results indicated that all methods report significant age and period effects, with lower obesity prevalence in early life as well as increasing prevalence in successive surveys. Positive cohort effects for more recently born cohorts emerged based on the constraint-based model; when cohort effects were considered second-order estimates, no significant effects emerged. First-order estimates of age-period-cohort effects are often criticized because of their reliance on arbitrary constraints, but may be conceptually meaningful for sociological research questions. Second-order estimates are statistically estimable and produce conceptually meaningful results for epidemiological research questions. Age-period-cohort analysts should explicitly state the definition of a cohort effect under consideration. Our analyses suggest that the prevalence of obesity in the U.S. in the latter part of the 20th century rose across all birth cohorts, in the manner expected based on estimated age and period effects. As such, the absence or presence of cohort effects depends on the conceptual definition and therefore statistical method used.

Socio-economic deprivation and survival of non-Hodgkin lymphoma in Scotland

Socio-economic deprivation is known to be associated with poorer survival from non-Hodgkin lymphoma (NHL) but routine data have not been able to determine whether this can be explained by differences in disease severity at presentation. We examined survival in all patients diagnosed with NHL in Scotland between 1979 and 1996 and between 1994 and 1996 used Scotland and Newcastle Lymphoma Group data, which include detailed clinical staging information. Compared with individuals from the most affluent areas, survival is 10% poorer in intermediate, and 19% poorer in patients living in the most deprived areas. Deprivation is associated with more B symptoms and poorer performance status but not with other indicators of more advanced disease, suggesting that the disease may be more aggressive or immunocompetence poorer among more deprived populations. We also noted improvements in relative survival from NHL over time.

Incidence of primary liver cancer in Italy between 1988 and 2002: an age-period-cohort analysis

We conducted in Italy a study to evaluate trends of primary liver cancer (PLC) and to disentangle the period from birth-cohort effects on PLC incidence. Cases aged<80 years and diagnosed between 1988 and 2002 in 20 areas covered by population-based Cancer Registries were included. Age-standardised incidence rates and age-period-cohort effects were estimated. In 1998-2002, incidence rates of PLC were 21.1/100,000 men and 6.0/100,000 women. In both genders, incidence rates increased slightly between 1988-1992 and 1993-1997 but did not rise thereafter. Amongst men, PLC risk increased in every cohort born after 1913 and the rise became steeper for cohorts born in 1948. In women, an upward trend appeared only in the cohorts born after 1953. Incidence of PLC over the last two decades in Italy did not substantially change but huge geographical variability emerged, mainly due to different times and modalities of spread of hepatitis C virus.

Incidence of Non-Hodgkin's Lymphoma in Sweden, Denmark, and Finland from 1960 through 2003: an Epidemic That Was

BACKGROUND

Reports during the early 1990s indicated non-Hodgkin's lymphoma (NHL) as one of the most rapidly increasing malignancies. More recent trends remain poorly characterized, as do the underlying reasons for NHL time trends, in particular, the effect of changes in classification and registration of lymphoproliferative malignancies. Insights into the descriptive epidemiology of NHL may shed light upon its elusive etiology.

METHODS

We used data from the Swedish, Danish, and Finnish national cancer registers to assess the incidences of NHL and other lymphoproliferative malignancies between 1960 and 2004. Using Poisson regression, we estimated the annual rate of change in NHL incidence per decade by sex, age, and country.

RESULTS

In Sweden, Denmark, and Finland, the NHL incidence increased in both genders and all age categories by about 4% every year up until the early 1990s. Thereafter, the incidence increased at a slower rate (ages 60-79 years), stabilized (ages 50-59 and > or =80 years), and decreased (ages 0-49 years), respectively, similarly for males and females in the three countries. Time trends of NHL were not reciprocated and explained by trends for other lymphoproliferative malignancies nor explained by trends in NHL as secondary primaries or NHL diagnosed postmortem.

CONCLUSIONS

The epidemic increase of NHL has recently subsided. Changes in the classification of lymphoproliferative malignancies, or occurrence of NHL as second primaries, only offer a marginal explanation.

Age-period-cohort analysis of suicide rates in Rio de Janeiro, Brazil, 1979-1998

BACKGROUND

Recent studies in Brazil have demonstrated that suicide rates have been rising over the last years. The objective of this study was to investigate trends in suicide from 1979 to 1998 in Rio de Janeiro State, with emphasis on age, period, and cohort effects.

METHOD

Age-specific suicide rates from 1979 to 1998 were estimated for males and females based on mortality data obtained from the Brazilian Mortality Information System, and population counts from the 1980, 1991 and 2000 censuses. Poisson regression and graphical methods were used to evaluate age, period and cohort effects.

RESULTS

Suicide rates increased steadily with age, particularly among males. In both males and females, age-adjusted suicide rates decreased until 1992. In 1993, rates started to rise. Cohort effects showed that younger generations had significantly lower rates of suicide than older ones.

CONCLUSION

The recent rise in suicide rates might be a result of the increasing levels of firearm availability, drug use, and unemployment. Follow-up over longer periods and powerful epidemiological studies are needed to sustain the implication of socio-economic changes in the observed features.

Secular trends in adolescent never smoking from 1990 to 1999 in California: an age-period-cohort analysis

OBJECTIVES

We analyzed age, time period, and cohort effects on trends in adolescent cigarette smoking in California from 1990 to 1999.

METHODS

Data from subjects aged 12 to 17 years (n = 26 536; 50.4% male) from the California Tobacco Survey and the California Youth Tobacco Survey were analyzed, and never smokers were used as the outcome measure.

RESULTS

The proportion of never smokers increased from 60% for males and 66% for females in 1990 to around 70% for both sexes in 1999. Respondents were more likely to be never smokers if born in 1978 or later (i.e., aged 12 years or younger in 1990, when most tobacco control programs started in California).

CONCLUSIONS

The statewide antitobacco programs prevented adolescents from starting to smoke, primarily through a cohort effect.

Going up or coming down? The changing phases of the lung cancer epidemic from 1967 to 1999 in the 15 European Union countries

Lung cancer, the most common cause of cancer death in the European Union (EU), continues to have an enormous impact on the health experience of the men and women living in the constituent countries. Information on the course of the lung cancer epidemic is essential in order to formulate an effective cancer control policy. This paper examines recent trends in lung cancer mortality rates in men and women in each of the 15 countries, comparing cross-sectional rates of death in younger (aged 30-64 years) and older populations (aged 65 years or over), and the age, period of death, and birth cohort influences in the younger age group. The latter analysis establishes the importance of year of birth, related to modifications in the tobacco habit among recently born generations. The stage of evolution of the lung cancer epidemic varies markedly by sex and country in terms of the direction, magnitude, and phase of development of national trends. In males, there is some consistency in the direction of the trends between EU countries, declines are apparent in most countries, at least in younger men, with rates in older men either reaching a plateau, or also falling. In younger persons, a decreasing risk of lung cancer death reflects changes in successive birth cohorts, due to modifications in the smoking habit from generation to generation, although these developments are in very different phases across countries. Portugal is the exception to the male trends; there are increases in mortality in both age groups, with little sign of a slowing down by birth cohort. In women, there are unambiguous upsurges in rates seen in younger and older women in almost all EU countries in recent decades, and little sign that the epidemic has or will soon reach a peak. The exceptions are the United Kingdom (UK) and Ireland, where lung cancer death rates are now declining in younger women and stabilising in older women, reflecting a declining risk in women born since about 1950. It is too early to say whether the observed plateau or decline in rates in women born very recently in several countries is real or random. To ascertain whether recent trends in lung cancer mortality will continue, trends in cigarette consumption should also be evaluated. Where data are available by country, the proportion of adult male smokers has, by and large, fallen steadily in the last five decades. In women, recent smoking trends are downwards in Belgium, Denmark, Sweden and the Netherlands, although in Austria and Spain, large increases in smoking prevalence amongst adults are emerging. Unambiguous public health messages must be effectively conveyed to the inhabitants of the EU if the lung cancer epidemic is to be controlled. It is imperative that anti-tobacco strategies urgently target women living in the EU, in order to halt their rapidly increasing risk of lung cancer, and prevent unnecessary, premature deaths among future generations of women.

Site- and gender-specific time trend analyses of the incidence of skin melanomas in the former German Democratic Republic (GDR) including 19351 cases

Over the past few decades, the incidence of skin melanoma has been rising in almost all developed countries. We examined trends in the incidence of skin melanoma in the former German Democratic Republic (GDR) from 1961 to 1989. Incidence rates per 100,000 person years were age-adjusted (World Standard Population). We estimated the effects of age, period, and cohort on the overall and site-specific incidence of skin melanoma. From 1961 to 1989, the incidence of melanoma increased from 1.8 to 5.0 for males and from 1.8 to 5.4 per 100,000 for females. Incidence was best explained by age, cohort and period effects. Incidence trends by anatomical site showed varying degrees of increases with the exception of melanomas of the eyelid that showed a decrease over time. Cohort effects differed by gender and anatomical site indicating that the circumstances leading to increasing site-specific incidences may have come into effect earlier for some sites than those for other sites.

Changing patterns of skin melanoma mortality in West Germany from 1968 through 1999

PURPOSE

Skin cancer incidence data from West Germany are available only for the territory of the Federal State of Saarland. We examined time trends in melanocytic and non-melanocytic skin cancer mortality for the territory of West Germany including a population of about 66 million people.

METHODS

We analyzed the melanocytic and non-melanocytic skin cancer mortality data (1968-99) from West Germany including West Berlin. We calculated age-specific and age-standardized mortality rates and used Poisson regression to estimate underlying age, cohort, and period effect.

RESULTS

The estimated percent annual increase of the skin melanoma mortality rate was 1.0% (95% CI, 0.7-1.3) among men and 0.5% (95% CI, 0.2-0.7) among women. This increase is mainly due to a rate increase in people aged 60 years or more. The skin melanoma mortality trend was best explained by age-, cohort-, and period effects. The risks increased in each successive birth cohort born between 1890 and roughly 1935. Thereafter, the risks declined through the most recent birth cohort born in 1975.

CONCLUSIONS

Skin melanoma mortality in West Germany showed an increase from 1968 through 1999 in people aged 60 years or more. The favorable mortality decline by birth cohort in the most recent birth cohort is an important indicator of a likely decline in mortality over the coming years.

Increasing incidence of non-Hodgkin's lymphoma in Canada, 1970-1996: age-period-cohort analysis

Previous studies have shown that the incidence of non-Hodgkin's lymphoma (NHL) has increased in many parts of the world in recent decades. Using data obtained from the Canadian Cancer Registry, the present study examined time trends in NHL incidence in Canada between 1970 and 1996 and the effects of age, period of diagnosis and birth cohort on incidence patterns for each sex separately. Results showed that overall age-adjusted incidence rates increased substantially, from 7.3 and 5.2 per 100,000 in 1970-1971 to 14.0 and 10.0 per 100,000 in 1995-1996 in males and females, respectively. Diffuse lymphoma was the major histological subtype, accounting for approximately 76% of NHL cases over the 27-year period. The data suggest that period effects have played a major role, although birth cohort effects may also have been involved. Sex-specific patterns of the incidence were similar over the time period of diagnosis but were distinct among recent birth cohorts. In conclusion, there is in fact a marked increase in NHL in Canada which cannot be explained in terms of improvements in diagnosis, changes in NHL classification and the increase in AIDS-associated NHL alone. The birth cohort effect in NHL suggests that changes in risk factors may have contributed to the observed increase.

Examination of temporal trends in the incidence of childhood leukaemias and lymphomas provides aetiological clues

The age-sex distributions and temporal trends in incidence of leukaemia and lymphoma from the Manchester Children's Tumour Registry (MCTR), 1954-1998, are reported. This 45-year study includes 1795 children, all of whom had a histologically and/or cytologically verified leukaemia or lymphoma. At the time of their diagnoses all the children were under 15 years of age and were resident in a geographically defined area of northwest England covered by the MCTR. Log-linear modelling identified significant linear increases in acute lymphoblastic leukaemia (ALL) (average annual increase 0.7%; P= 0.005) and in Hodgkin's disease (HD) (1.2%, P=0.04), but not in acute myeloid leukaemia (AML), nor in non-Hodgkin's lymphoma (NHL). The increase in ALL was most pronounced amongst males, aged 1-4 years, and is likely to be due to precursor B-cell leukaemias. The increases in ALL and HD are discussed in relation to current hypotheses suggesting a role for infection. Additionally, a non-linear cohort effect was identified for NHL (P= 0.008), which may indicate the involvement of environmental factors other than infection.

Temporal increases in the incidence of childhood solid tumors seen in Northwest England (1954-1998) are likely to be real

BACKGROUND

There has been speculation that increasing trends in incidence of childhood central nervous system tumors and infant neuroblastoma in the United States have been due to diagnostic improvements or reporting changes. To investigate whether or not such trends could be explained in this way in the U.K., the authors used population-based data from Northwest England to analyze incidence trends in childhood solid tumors.

METHODS

Cases were diagnosed during 1954-1998 and were grouped according to a morphology-based classification scheme. More than 95% of diagnoses were based on special histopathologic review. Tissue sections were retained, and diagnoses were rereviewed to ensure consistency in classification throughout the time period. Age-, gender- and period-specific incidence rates were calculated. Analyses were performed with chi-square tests and Poisson regression.

RESULTS

There was an overall increase in the incidence of all childhood solid tumors of 0.9% each year. A temporal increase was found in childhood brain tumors characterized by, in particular, annual increases of 1% in pilocytic astrocytoma, 1% in primitive neuroectodermal tumors, and 2.3% in miscellaneous gliomas. The incidence of germ cell tumors increased at a rate of 2.6% each year.

CONCLUSIONS

These increases could not be attributed to changes in diagnostic practice, and it is unlikely that the increases were due to changes in reporting practice. Further, the restriction of the increases to certain groups, with stable rates in others, argued against the changes being artifactual. The authors concluded that the increases in incidence were likely to be real.

Age-period-cohort analysis of dentist use in Spain from 1987 to 1997. An analysis based on the Spanish National Health Interview Surveys

The aim was to determine whether the effects of age, period (from 1987 to 1997), or cohort (birth-cohort) are the most plausible explanations for the variation in dentist utilisation over time in Spain. On the basis of three sequential Spanish National Health Surveys, the trend in the percentage of people visiting the dentist within the previous 3 months was analysed by means of a standard cohort table and by the CLAYTON & SCHIFFLERS method. The percent of people visiting the dentist grew from 13.6% in 1987, to 17.2% in 1997. Visual examination of the cohort table, together with the fit of the age-cohort model, indicates that cohort succession may be the best explanation for the increase. The younger the cohort, the higher the dental visit rate; this relationship was strongest for people born after 1977. The model also indicates that the rates of dental visiting tend to increase up to middle age, and then tend to decrease with age.

Age-period-cohort models: a comparative study of available methodologies

This article compares the estimates produced by a number of solutions to the identifiability problem in age-period-cohort models using a series of disease rates with known structure. The results suggest that only those methods that are based on the estimable functions such as curvatures can be recommended for use in all circumstances. The other common approaches that give parameter estimates that are easier to interpret all have induced bias in the estimates. In particular methods based on the minimization of a penalty function to achieve identifiability are only of use if there is no change in the rates with time. Any drift in the rates tends to be expressed as a cohort-based trend. The methods based on individual records introduce a bias if there is a strong age effect in the direction of a decreasing cohort trend and a compensating increase based on period effects. The nonparametric testing method has little power to detect trends in the rates in small tables but ascribes a strong drift in the rates to both period and cohort trends. With careful interpretation, all methods estimate nonlinear components correctly.

The rise in incidence of lymphomas in Europe 1985-1992

A collaborative study was carried out of the descriptive epidemiology of the lymphomas from seven countries across Europe in the period 1985-1992. Careful attention was paid to sources of information and the data quality in close collaboration with expert histopathologists. The data were classified as non-Hodgkin's lymphoma (NHL) and Hodgkin's disease (HD). An attempt was made to put the data into a modified version of the Revised European American Lymphoma (REAL) classification. We observed an overall rise in total NHL throughout the time period in all European countries but no such trend in HD. The increase in NHL overall being 4.2% per annum, representing an increase of 4.8% in males and 3.4% in females per annum, was only marked in middle and old age. Such increases were observed in all participating areas except in Burgundy. Different countries, however, have different base rates, the rates being highest in Scandinavia and the Netherlands. The analysis by subcategory classification suggested that the increase in NHL was confined to the follicle centre cell type, extranodal B-cell, nodal T-cell and nodal lymphomas not otherwise specified, categories. These new observations present a picture of real increase in case incidence with no obvious explanation. The increases in NHL do not appear to be due solely to better diagnoses. Pending other explanations or refutation, these present a compelling picture of an inexorable rise in incidence of this disease.

Descriptive epidemiology of gastrointestinal non-Hodgkin's lymphoma in a population-based registry

The incidence of non-Hodgkin's lymphoma (NHL), particularly at certain extranodal sites, has been demonstrated to be rising, at least in the USA, more than for any other malignancy. One of the major sites of extranodal NHL is the gastrointestinal tract, though little is known of its epidemiological characteristics. Over an 8-year period (1986 to 1993) 1069 primary gastrointestinal NHL cases were reported to the Leukaemia Research Fund Data Collection Survey which covers many parts of England and Wales. Age-standardized incidence rates of gastrointestinal NHL at all sites (0.58/10(5) per year), gastric (0.24/10(5) per year), small bowel (0.17/10(5) per year) and large bowel (0.06/1(5) per year) confirmed that the UK has the lowest rates of gastrointestinal NHL in Europe. An excess of males was observed at all ages and for all sites. Time-trend analyses showed annual increases in incidence rates for gastric (6.3%) and small bowel (5.9%) NHL although a concomitant decrease in gastrointestinal NHL of unknown site suggested that at least part of these increases had resulted from more accurate diagnoses. Overall, the incidence of gastrointestinal NHL significantly increased by 2.7% per annum and was limited to the population aged over 50 years in this series.

Cancer mortality in Europe: effects of age, cohort of birth and period of death

Death certification data for 19 cancers or groups of cancers, plus total cancer mortality, in 16 major European countries were analysed using a log-linear Poisson model with arbitrary constraints on the parameters to disentangle the effects of age, birth cohort and period of death. Three major patterns emerged including: first, the prominent role of cohort of birth in defining trends in mortality from most cancer sites (except testis or Hodgkin's disease, where newer treatments had a major period of death effect); and second, the major role of lung and other tobacco-related neoplasm epidemics in determining the diverging pattern of cancer mortality, for each sex and in various European countries and geographic areas. In most countries, the peak male cohort values were reached for generations born between 1900 and 1930. This was observed in women only for Denmark and the U.K., i.e. the two countries where lung and other tobacco-related neoplasm epidemics had already reached appreciable levels. This confirms the importance of cigarette smoking in subsequent generations as a major cause of cancer deaths in Europe. Further, there is a persistent rise in several cancer rates, again chiefly on a cohort basis, in Eastern Europe, which calls for urgent intervention to control the cancer burden in these countries.