Analysis of household data on influenza epidemic with Bayesian hierarchical model

Data used for modelling the household transmission of infectious diseases, such as influenza, have inherent multilevel structures and correlated property, which make the widely used conventional infectious disease transmission models (including the Greenwood model and the Reed-Frost model) not directly applicable within the context of a household (due to the crowded domestic condition or socioeconomic status of the household). Thus, at the household level, the effects resulting from individual-level factors, such as vaccination, may be confounded or modified in some way. We proposed the Bayesian hierarchical random-effects (random intercepts and random slopes) model under the context of generalised linear model to capture heterogeneity and variation on the individual, generation, and household levels. It was applied to empirical surveillance data on the influenza epidemic in Taiwan. The parameters of interest were estimated by using the Markov chain Monte Carlo method in conjunction with the Bayesian directed acyclic graphical models. Comparisons between models were made using the deviance information criterion. Based on the result of the random-slope Bayesian hierarchical method under the context of the Reed-Frost transmission model, the regression coefficient regarding the protective effect of vaccination varied statistically significantly from household to household. The result of such a heterogeneity was robust to the use of different prior distributions (including non-informative, sceptical, and enthusiastic ones). By integrating out the uncertainty of the parameters of the posterior distribution, the predictive distribution was computed to forecast the number of influenza cases allowing for random-household effect.

Abstract S1-10: Disparities in the estimates of benefits and harms from mammography: Are the numbers really different?

It is generally accepted that screening with mammography prevents deaths from breast cancer, although debate continues about the absolute size of the mortality benefit, and the concomitant risks associated with screening. A number of recent observational studies have claimed to find low rates of benefit in terms of reducing mortality rates or late stage disease, and high rates of overdiagnosis, defined as the diagnosis by screening of cancer which would not have been diagnosed in the patient's lifetime if screening had not taken place. These publications have achieved a high profile in the mass media and stimulated further debate. We review the apparent disparities between different reviews of the effects of mammography screening on mortality from breast cancer and on overdiagnosis. The four major reviews are the UK Independent Review, the Nordic Cochrane review, the US Preventive Services Task Force (USPSTF) review, and the EUROSCREEN review. The estimated number needed to screen/invite to prevent one death from breast cancer ranges from 111 to 2000, almost a 20-fold range. The estimated number required varies by age group, whether the intervention described is actual screening or invitation to screening, follow-up time and other factors. To assess whether these represent genuine disagreements or whether the differences are mainly due to such factors as follow-up time and target population, we converted all four to pertain to the same scenario as used in the UK Independent Review, that is to the effect of screening for 20 years from age 50 to 69 on breast cancer mortality in ages 55-79, in a UK population. When all four reviews are converted to the UK review scenario, the range of absolute benefits is now only 2.5-fold rather than 20-fold. Thus, the differences between the reviews with respect to the absolute breast cancer mortality reduction are almost entirely due to expressing the same basic result relative to different denominators, choice of population mortality rates, etc. Thus, the so-called controversy over the benefit of mammography screening as estimated from the trials is largely contrived. When expressed relative to the same denominator, with the same screening and follow-up periods, and using the same absolute mortality rates, absolute benefit estimates are all of the same order of magnitude, and all indicate a substantial reduction in breast cancer mortality with screening. While there are genuine disagreements about overdiagnosis, methods which adjust for lead time and underlying incidence trends yield estimates which are modest and are outweighed by the mortality benefit.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr S1-10.

Differences in Endpoints between the Swedish W-E (Two County) Trial of Mammographic Screening and the Swedish Overview: Methodological Consequences

Objectives

To characterize and quantify the differences in the number of cases and breast cancer deaths in the Swedish W-E Trial compared with the Swedish Overview Committee (OVC) summaries and to study methodological issues related to trials in secondary prevention.

Setting

The study population of the W-E Trial of mammography screening was included in the first (W and E county) and the second (E-county) OVC summary of all Swedish randomized mammography screening trials. The OVC and the W-E Trial used different criteria for case definition and causes of death determination.

Method

A Review Committee compared the original data files from Wand E county and the first and second OVC. The reason for a discrepancy was determined individually for all non-concordant cases or breast cancer deaths.

Results

Of the 2615 cases included by the W-E Trial or the OVC, there were 478 (18%) disagreements. Of the disagreements 82% were due to inclusion/exclusion criteria, and 18% to disagreement with respect to cause of death or vital status at ascertainment. For E-County, the OVC inclusion rules and register based determination of cause of death (second OVC) rather than individual case review (W-E Trial and 1st OVC) resulted in a reduction of the estimate of the effect of screening, but for W-County the difference between the original trial and the OVC was modest.

Conclusions

The conclusion that invitation to mammography screening reduces breast cancer mortality remains robust. Disagreements were mainly due to study design issues, while disagreements about cause of death were a minority. When secondary research does not adhere to the protocols of the primary research projects, the consequences of such design differences should be investigated and reported. Register linkage of trials can add follow-up information. The precision of trials with modest size is enhanced by individual monitoring of case status and outcome status such as determination of cause of death.