Exposure measurement in case-control studies: reported methods and recommendations

Financial Performance Under the Influence of the Coronavirus Disease 2019: Effects of Strategic Flexibility and Environmental Dynamics in Big Data Capability

This study draws on the dynamic capabilities view and the firm’s big data capability (BDC) in the new economic environment. It constructs an adjusted intermediary model to study the mechanism of BDC, strategic flexibility, and environmental dynamic affecting financial performance. We find that strategic flexibility plays an intermediary role in the “Converse-U” relationship between BDC and financial performance. Environmental dynamics adjust the relationship between BDC and financial performance positively and smooth the “Converse-U” relationship. The findings suggest building and managing BDC, combining BDC with the management process, and achieving continuous financial performance improvement in a dynamic environment. The paper also puts forward the nonlinear hypothesis, discusses the “Converse-U” relationship between BDC and enterprise financial performance in the Chinese context of digital economy explosion and growth, and considers the intermediary mechanism of strategic flexibility and the regulatory effect of environmental dynamics.

Assessment of occupational risks to extremely low frequency magnetic fields: Validation of an empirical non-expert approach

The expert method of exposure assignment involves relying on chemists or hygienists to estimate occupational exposures using information collected on study subjects. Once the estimation method for a particular contaminant has been made available in the literature, it is not known whether a non-expert, briefly trained by an expert remaining available to answer ad hoc questions, can provide reliable exposure estimates. We explored this issue by comparing estimates of exposure to extremely low frequency magnetic fields (ELF-MF) obtained by an expert to those from a non-expert. Using a published exposure matrix, both the expert and non-expert independently calculated a weekly time-weighted average exposure for 208 maternal jobs by considering three main determinants: the work environment, magnetic field sources, and duration of use or exposure to given sources. Agreement between assessors was tested using the Bland-Altman 95% limits of agreement. The overall mean difference in estimates between the expert and non-expert was 0.004 μT (standard deviation 0.104). The 95% limits of agreement were − 0.20 μT and + 0.21 μT. The work environments and exposure sources were almost always similarly identified but there were differences in estimating exposure duration. This occurred mainly when information collected from study subjects was not sufficiently detailed. Our results suggest that following a short training period and the availability of a clearly described method for estimating exposures, a non-expert can cost-efficiently and reliably assign exposure, at least to ELF-MF.

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Retrospective occupational exposure assessment often relies on the expert method.

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Using a published job-exposure matrix, a trained non-expert can correctly estimate an individual's specific exposure.

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Non-expert method is a feasible, practical, and based on our study, a valid approach to code exposure.

Epidemiology research in rheumatology-progress and pitfalls

Epidemiology research is a vital component of clinical studies in all medical fields. This Review provides a brief introduction to the methodology and interpretation of population and clinical epidemiology studies of musculoskeletal disorders. Data sources (including 'big data' and the issue of missing data), study design (cross-sectional, case-control and cohort studies, including clinical trial design) and the interpretation of study results are discussed with examples from the field of rheumatology, particularly using findings in patients with rheumatoid arthritis. Two or more treatments can be compared in clinical trials using a variety of study designs including superiority, noninferiority or equivalence. The different types of risk in epidemiological studies-absolute, attributable, background and relative-are important concepts in epidemiological research and their relative usefulness to clinicians and patients should be considered carefully. The potential pitfalls and challenges of generalizing the results of epidemiological studies to understanding disease aetiology and to clinical practice are also emphasized. The aim of the Review is to help readers to critically appraise published articles that use epidemiological designs or methods.

Barriers, motivators and facilitators related to prenatal care utilization among inner-city women in Winnipeg, Canada: a case-control study

BACKGROUND

The reasons why women do not obtain prenatal care even when it is available and accessible are complex. Despite Canada's universally funded health care system, use of prenatal care varies widely across neighborhoods in Winnipeg, Manitoba, with the highest rates of inadequate prenatal care found in eight inner-city neighborhoods. The purpose of this study was to identify barriers, motivators and facilitators related to use of prenatal care among women living in these inner-city neighborhoods.

METHODS

We conducted a case-control study with 202 cases (inadequate prenatal care) and 406 controls (adequate prenatal care), frequency matched 1:2 by neighborhood. Women were recruited during their postpartum hospital stay, and were interviewed using a structured questionnaire. Stratified analyses of barriers and motivators associated with inadequate prenatal care were conducted, and the Mantel-Haenszel common odds ratio (OR) was reported when the results were homogeneous across neighborhoods. Chi square analysis was used to test for differences in proportions of cases and controls reporting facilitators that would have helped them get more prenatal care.

RESULTS

Of the 39 barriers assessed, 35 significantly increased the odds of inadequate prenatal care for inner-city women. Psychosocial issues that increased the likelihood of inadequate prenatal care included being under stress, having family problems, feeling depressed, "not thinking straight", and being worried that the baby would be apprehended by the child welfare agency. Structural barriers included not knowing where to get prenatal care, having a long wait to get an appointment, and having problems with child care or transportation. Attitudinal barriers included not planning or knowing about the pregnancy, thinking of having an abortion, and believing they did not need prenatal care. Of the 10 motivators assessed, four had a protective effect, such as the desire to learn how to protect one's health. Receiving incentives and getting help with transportation and child care would have facilitated women's attendance at prenatal care visits.

CONCLUSIONS

Several psychosocial, attitudinal, economic and structural barriers increased the likelihood of inadequate prenatal care for women living in socioeconomically disadvantaged neighborhoods. Removing barriers to prenatal care and capitalizing on factors that motivate and facilitate women to seek prenatal care despite the challenges of their personal circumstances may help improve use of prenatal care by inner-city women.

Case-control studies of sporadic enteric infections: a review and discussion of studies conducted internationally from 1990 to 2009

Epidemiologists have used case-control studies to investigate enteric disease outbreaks for many decades. Increasingly, case-control studies are also used to investigate risk factors for sporadic (not outbreak-associated) disease. While the same basic approach is used, there are important differences between outbreak and sporadic disease settings that need to be considered in the design and implementation of the case-control study for sporadic disease. Through the International Collaboration on Enteric Disease "Burden of Illness" Studies (the International Collaboration), we reviewed 79 case-control studies of sporadic enteric infections caused by nine pathogens that were conducted in 22 countries and published from 1990 through to 2009. We highlight important methodological and study design issues (including case definition, control selection, and exposure assessment) and discuss how approaches to the study of sporadic enteric disease have changed over the last 20 years (e.g., making use of more sensitive case definitions, databases of controls, and computer-assisted interviewing). As our understanding of sporadic enteric infections grows, methods and topics for case-control studies are expected to continue to evolve; for example, advances in understanding of the role of immunity can be used to improve control selection, the apparent protective effects of certain foods can be further explored, and case-control studies can be used to provide population-based measures of the burden of disease.

Inter-rater reliability of assessed prenatal maternal occupational exposures to solvents, polycyclic aromatic hydrocarbons, and heavy metals

Because direct measurements of past occupational exposures are rarely available in population-based case-control studies, exposure assessment of job histories by multiple expert raters is frequently used; however, the subjective nature of this method makes measuring reliability an important quality control step. We evaluated inter-rater reliability of 7729 retrospective jobs reported in the National Birth Defects Prevention Study. Jobs were classified as exposed, unexposed, or exposure unknown by two independent industrial hygienists; exposed jobs were further evaluated for intensity, frequency, and routes. Exposure prevalence ranged from 0.1-9.8%. Inter-rater reliability for exposure (yes/no), assessed by kappa coefficients, was fair to good for cadmium (κ = 0.46), chlorinated solvents (κ = 0.59), cobalt (κ = 0.54), glycol ethers (κ = 0.50), nickel compounds (κ = 0.65), oil mists (κ = 0.63), and Stoddard Solvent (κ = 0.55); PAHs (κ = 0.24) and elemental nickel (κ = 0.37) had poor agreement. After a consensus conference resolved disagreements, an additional 4962 jobs were evaluated. Inter-rater reliability improved or stayed the same for cadmium (κ = 0.51), chlorinated solvents (κ = 0.81), oil mists (κ = 0.63), PAHs (κ = 0.52), and Stoddard solvent (κ = 0.92) in the second job set. Inter-rater reliability varied by exposure agent and prevalence, demonstrating the importance of measuring reliability in studies using a multiple expert rater method of exposure assessment.

Father's occupational exposure to carcinogenic agents and childhood acute leukemia: a new method to assess exposure (a case-control study)

Background

Medical research has not been able to establish whether a father's occupational exposures are associated with the development of acute leukemia (AL) in their offspring. The studies conducted have weaknesses that have generated a misclassification of such exposure. Occupations and exposures to substances associated with childhood cancer are not very frequently encountered in the general population; thus, the reported risks are both inconsistent and inaccurate. In this study, to assess exposure we used a new method, an exposure index, which took into consideration the industrial branch, specific position, use of protective equipment, substances at work, degree of contact with such substances, and time of exposure. This index allowed us to obtain a grade, which permitted the identification of individuals according to their level of exposure to known or potentially carcinogenic agents that are not necessarily specifically identified as risk factors for leukemia. The aim of this study was to determine the association between a father's occupational exposure to carcinogenic agents and the presence of AL in their offspring.

Methods

From 1999 to 2000, a case-control study was performed with 193 children who reside in Mexico City and had been diagnosed with AL. The initial sample-size calculation was 150 children per group, assessed with an expected odds ratio (OR) of three and a minimum exposure frequency of 15.8%. These children were matched by age, sex, and institution with 193 pediatric surgical patients at secondary-care hospitals. A questionnaire was used to determine each child's background and the characteristics of the father's occupation(s). In order to determine the level of exposure to carcinogenic agents, a previously validated exposure index (occupational exposure index, OEI) was used. The consistency and validity of the index were assessed by a questionnaire comparison, the sensory recognition of the work area, and an expert's opinion.

Results

The adjusted ORs and 95% confidence intervals (CI) were 1.69 (0.98, 2.92) during the preconception period; 1.98 (1.13, 3.45) during the index pregnancy; 2.11 (1.17, 3.78) during breastfeeding period; 2.17 (1.28, 3.66) after birth; and 2.06 (1.24, 3.42) for global exposure.

Conclusion

This is the first study in which an OEI was used to assess a father's occupational exposure to carcinogenic agents as a risk factor for the development of childhood AL in his offspring. From our results, we conclude that children whose fathers have been exposed to a high level of carcinogenic agents seem to have a greater risk of developing acute leukemia. However, confounding factors cannot be disregarded due to an incomplete control for confounding.

Interviewer variability - quality aspects in a case-control study

Quality assurance and quality control are important for the reliability of case-control studies. Here we describe the procedures used in a previously published study, with emphasis on interviewer variability. To evaluate risk factors for acute pancreatitis, information including previous diagnoses and medication was collected from medical records and by telephone interviews from 462 cases and 1781 controls. Quality assurance procedures included education and training of interviewers and data validity checks. Quality control included a classification test, annual test interviews, expert case validation, and database validation. We found pronounced variations between interviewers. The maximal number of interviews per day varied from 3 to 9. The adjusted average (95% CI) number of diagnoses captured per interview of cases was 4.1 (3.8-4.3) and of controls 3.5 (3.4-3.7) (excluding one deviating interviewer). For drugs, the average (95% CI) number per interview was 3.9 (3.7-4.1) for cases and 3.3 (3.2-3.4) for controls (excluding one deviating interviewer). One of the fourteen interviewers deviated significantly from the others, and more so for controls than for cases. This interviewer's data ;were excluded. Nonetheless, data concerning controls more frequently needed correction and supplementation than for cases. Erroneous coding of diagnoses and medication was also more frequent among controls. Thus, a system for quality control of coding practices is crucial. Variability in interviewers' ability to ascertain information is a possible source of bias in interview-based case-control studies when "blinding" cannot be achieved.

Farm Family Exposure Study: methods and recruitment practices for a biomonitoring study of pesticide exposure

PURPOSE

The Farm Family Exposure Study was initiated to characterize pesticide exposure to farm family members around the time of one pesticide application in a manner that will facilitate exposure assessment in epidemiologic studies of pesticides.

METHODS

A sample of farm families with children was recruited by randomly selecting farmers from lists of licensed pesticide applicators in Minnesota and South Carolina. Eligible families were selected from among those who planned to apply one of three chemicals, glyphosate, 2,4-D, or chlorpyrifos, as part of their normal operations. The applicator, spouse, and all children in the family ages 4-17 years were included in the study. The applicator and spouse completed self-administered questionnaires addressing demographics, farming practices and potential exposures to them and their children. Field observers documented the application, recorded application practices, equipment, potential exposures, and the presence of children or spouses in the immediate vicinity of pesticide activities. All study participants were asked to collect each urine void for 5 days, 1 day before through 3 days after the application. Pesticides were measured in 24-h composite urine samples with a one part per billion limit of detection.

RESULTS

Of 11,164 applicators screened, 994 families met the inclusion criteria. Of these, 95 families were enrolled. Enrollees were similar in most characteristics to their peers who were not participants in the study. In total, there were 106 applications, 10 of which involved more than one chemical. This resulted in urinary data for 48 farmers and spouses and their 79 children for glyphosate, 34 farmers and spouses and their 50 children for chlorpyrifos, and 34 farmers and spouses and their 53 children for 2,4-D. Compliance with the 24-h urine collection was particularly good for the adult participants. There were more missing samples for children than for adults, but overall compliance was high.

CONCLUSION

The Farm Family Exposure Study should provide insights about pesticide exposure under real world conditions and thereby facilitate improved exposure assessment in epidemiologic studies of agricultural populations.

Student–parent agreement in self-reported sun behaviors

OBJECTIVE

We sought to describe agreement between parent proxy and student self-reported sun behaviors and sun protective practices in adolescents aged 10 to 14 years.

METHODS

We conducted a cross-sectional pilot study of students (n = 52) from two classrooms, grades 6 and 7, at a school system in Framingham, Mass. Data were collected using self-administered questionnaires. Students were asked to report their sun behaviors and sun protective practices. Proxy measures were obtained by asking parents to report sun behaviors and practices of their children. Agreement was measured using weighted kappa analysis for ordinal data. Mean differences (95% confidence intervals) were calculated.

RESULTS

The response rate for student/proxy pairs was 96% (n = 50). Agreement between student and proxy was good for skin color, sunscreen use, number of sunburns in the past summer, and application of sunscreen while in other outdoor places (range kappa = 0.52-0.73). Lowest agreement was found for questions relating to wearing a shirt, wearing a hat, sitting in the shade, and frequency of parental sunscreen application to the students' backs (range kappa = 0.08-0.28). Mean differences in responses between student and proxy respondents were relatively small ranging from -0.39 to +0.25.

CONCLUSIONS

The lack of a gold standard in the assessment of sun exposure and related sun protective practices limits the ability to validate these exposure measures in skin cancer studies. The assessment of sun exposure behaviors is especially problematic when relying on a child's ability to accurately recall these exposures. Parent proxy measures are often used as surrogate measures and for validation purposes. We found low to moderate student/proxy agreement in this pilot study suggesting that adolescents can effectively recall their recent sun behaviors and protective practices when compared with parent proxy measures.

Occupational exposure assessment in case-control studies: opportunities for improvement

Community based case-control studies are an efficient means to study disease aetiologies, and may be the only practical means to investigate rare diseases. However, exposure assessment remains problematic. We review the literature on the validity and reliability of common case-control exposure assessment methods: occupational histories, job-exposure matrices (JEMs), self reported exposures, and expert assessments. Given the variable quality of current exposure assessment techniques, we suggest methods to improve assessments, including the incorporation of hygiene measurements: using data from administrative exposure databases; using results of studies identifying determinants of exposure to develop questionnaires; and where reasonable given latency and biological half life considerations, directly measuring exposures of study subjects.

An unmatched case-control study of nearly lethal suicide attempts in Houston, Texas: research methods and measurements

This article details the research methods and measurements used in conducting a population-based, case-control study of nearly lethal suicide attempts among persons aged 13-34 years, residing in Houston, Texas. From November 1992 to July 1995, we interviewed 153 case subjects presenting at one of three participating hospital emergency departments and used random digit dialing to identify 513 control subjects residing in the same catchment area in which cases were enlisted. Unlike most research in this area, this study was designed to extend our understanding of suicidal behavior and prevention activities beyond identification and treatment of depression and other mental illnesses. We discuss the overall strengths and weaknesses of our study design and conclude that this methodology is well suited for studying rare outcomes such as nearly lethal suicide.

A case-referent study of cancer mortality among sulfate mill workers in Sweden

OBJECTIVES

To investigate whether workers in Swedish sulfate mills have an increased risk of death from certain malignancies that have previously been linked to the pulping process.

METHODS

Subjects of the study (n=2480) were men aged 40-75 at death during 1960-89 in the parishes surrounding four sulfate mills. Exposure assessment was based on information from the personnel files in the mills- 35% of the subjects were recognised there, and work categories were created.

RESULTS

Among all sulfate mill workers, the odds ratio (OR) (90% confidence interval (90% CI)) for death from lung cancer was 1.6 (1.1 to 2.3), pleural mesotheliomas 9.5 (1.9 to 48), brain tumours 2.6 (1.2 to 5.3), and liver or biliary tract cancer 2.3 (1.0 to 5.2). There was an increased mortality from leukaemia among workers in the soda recovery plant (5.9 (2.6 to 13)) and bleaching plant and digester house (2.8 (1.0 to 7.5)).

CONCLUSIONS

Sulfate mill workers were at increased risk of dying from lung cancer and pleural mesotheliomas, probably due to exposure to asbestos. Increased risks of brain tumours and cancers of the liver or biliary tract were also found but the aetiology is not obvious.

Assessment of occupational exposures in community-based case-control studies

Assessing occupational exposures in community-based studies is a challenge for investigators because there are no standardized or validated approaches for collecting information regarding occupational history. The strengths and limitations of the methods available for assessing occupational exposures are reviewed. In community-based case-control studies, the prevalence of most chemical agents is low. The common sources of misclassification in these studies are addressed, as are strategies for dealing with misclassification bias. Methods to assess the presence and magnitude of differential reporting by cases and controls are outlined, together with analytic strategies to improve the classification of occupational exposures.

Biostatistics in the new millennium: a consulting statistician's perspective

This article attempts to predict the future for biostatistics and biostatisticians in the twenty-first century. Life will certainly be more complex and there will be growth in population, large corporations, and globalization generally. However, there will continue to be problems relating to biology, medicine, health and the environment, so biostatisticians can surely play an important role, if they are willing to adapt to changing circumstances. Personal views are expressed concerning those areas of most recent development that seem likely to be continued in the coming years: applications (clinical trials, epidemiology, vital statistics), philosophies, models, advances in computing, and the profession of biostatistics.

Assessment of occupational exposures in a general population: comparison of different methods

OBJECTIVES

To evaluate the relative merits of job specific questionnaires and various alternative assessment methods of occupational exposures often used in general population studies.

METHODS

Subjects were participants in a hospital based case-control study of risk factors for male infertility. Estimates of exposure to organic solvents and chromium, based on job specific questionnaires, generic questionnaires, self reports of exposure, an external job exposure matrix (JEM), and a population specific JEM were compared with passive diffuse dosimeter results and measurements in urine. Urine samples from the end of the shift were analysed for metabolites of toluene, xylene, several glycol ethers, trichloroethylene, and chromium. Passive dosimeter date, metabolites of specific solvents, and urinary chromium concentrations were available for 89, 267, and 156 subjects, respectively. The alternative methods and measurements in urine were compared by means of the Cohen's kappa statistic and by computing the positive predictive value, sensitivity, and specificity of the alternative methods against measurements in urine.

RESULTS

Passive dosimeter results indicated that exposure classifications with job specific questionnaire information could discriminate between high and low exposures. The kappa coefficients were < 0.4, so agreement between the various methods and measurements in urine was poor. Sensitivity of the methods ranged from 0.21 to 0.85, whereas specificity ranged from 0.34 to 0.94. Positive predictive values ranged from 0.19 to 0.58, with the highest values for job specific questionnaires.

CONCLUSIONS

The results indicate that the implementation of job specific questionnaires in a general population study might be worth the extra expense it entails, bearing in mind the paramount importance of avoiding false positive exposure estimates when exposure prevalence is low.

Chemicals and menopause: effects on age at menopause and on health status in the postmenopausal period

Menopause, a natural stage in women's lives, signals the cessation of fertility and causes changes in health status for many women. Chemical exposures may induce early or premature menopause and increase the risks of morbidity and mortality in the postmenopausal period. Chemicals that are toxic to follicles can lower the age of menopause by depleting the ovary of oocytes. Women may be exposed to these chemicals in the workplace, at home, and through exposure to contaminated drinking water near hazardous waste sites, as well as by direct or indirect exposure to cigarette smoke.

Measurement errors stemming from nonrespondents present at in-person interviews

PURPOSE

Data are frequently collected from in-person interviews in epidemiologic studies. Despite the advantages of this mode of data collection, the presence of a third party during the interview can contribute to measurement error, especially if third-party presence is related to case status.

METHODS

Using data obtained from a case-control study of colon cancer, we evaluated the frequency of third-party presence during in-person interviews, and how having someone else present during the interview influences reporting of exposure data.

RESULTS

Interviews were conducted in the presence of a third party for 28% of cases and 22% of controls who lived in a household of two or more individuals. Men with a third party present reported significantly lower age-adjusted mean levels of alcohol consumption (P < 0.01). Associations, as indicated by odds ratios, between colon cancer and alcohol intake were not statistically different among those with a third party present and those without a third party present. Although not statistically significant, energy intake was more strongly associated with colon cancer among those without a third party present during the interview.

CONCLUSIONS

These results emphasize the need to review questions to be asked and decide whether privacy should be emphasized before data collection begins. If privacy is required, interviewers need to be given better skills to ensure privacy during interview.

Statistics in epidemiology: the case-control study

This article presents a general review of the major trends in the conceptualization, development, and success of case-control methods for the study of disease causation and prevention. "Recent work on nested case-control, case-cohort, and two-stage case control designs demonstrates the continuing impact of statistical thinking on epidemiology. The influence of R. A. Fisher's work on these developments is mentioned wherever possible. His objections to the drawing of causal conclusions from observational data on cigarette smoking and lung cancer are used to introduce the problems of measurement error and confounding bias."

Use and misuse of statistics for epidemiological studies of multiple sclerosis

Despite a vast literature on the epidemiology of multiple sclerosis, the cause of this disease remains elusive. The majority of the studies have focused on prevalence, so that a worldwide distribution of multiple sclerosis can now be mapped. Tantalizing apparent differences in prevalence have resulted in an abundance of hypotheses about risk factors for multiple sclerosis, none of which have been firmly established. This article reviews the difficulties inherent in the use of any type of descriptive study to investigate etiology of disease and provides an update of appropriate statistical methodology to analyze study results. The major focus is on the use of analytical study design, specifically the case-control study, to investigate a specific hypothesis about association between a risk factor and multiple sclerosis. An update on new epidemiological and statistical methodology to enhance the design of future case-control studies is presented. Future opportunities to study multiple sclerosis in new ways, such as in cohort studies or nested case-control studies, using large medical insurance and other types of health-related data bases, are discussed.