Bias in Case-Control Studies of Screening Effectiveness

Abstract

Screening programs, such as annual mammography, are undertaken to reduce mortality and/or morbidity from chronic diseases such as cancer. Matched case-control studies have been used to assess the effectiveness of screening programs because of their relative simplicity and low cost. In such studies, the exposure history for controls consists of the number of screening examinations received prior to the date of diagnosis of the matched case. The authors know of no methodological evaluations that demonstrate the validity of such case-control studies. To examine the possible existence of bias due to design rules, the authors developed a simple deterministic model, which is used to calculate expected screening and disease patterns in a cohort. Cases and matched controls are selected from the cohort, and their screening histories are used to calculate an odds ratio, as is commonly done in practice. Results utilizing this simple model suggest that systematic inclusion of the examination from which diagnosis is made, which is the approach typically used in practice, leads to a positive bias (odds ratio > 1) in the absence of any real effect. Systematic exclusion of this examination appears to lead to a negative bias (odds ratio < 1). Although this simple approach has several limitations, the results suggest that a commonly used method of conducting case-control studies may yield biased odds ratios. Possible methods to reduce this bias may exist, such as defining exposure intervals differently.

Seventeen-year evaluation of breast cancer screening: the DOM project, The Netherlands

“…from which the diaenosis was made. in the screenin2 history of the screen-detected cases (Hosek et al 1996) appears to be present in the current study. Its effect is reflected in an OR of 0.54 (with inclusion of the diagnostic screening: 95C% confidence interval 0.37-0.79) and 0.38 (without screening: 95%7s confidence interval 0.26-0.56).…”

“…The unbiased OR may be expected to lie between the two estimates. because systematic exclusion of the screening examination can cause bias in the opposite direction to that of its inclusion (Hosek et al 1996). The other form of bias.…”

“…bv means of a nested case-control studv. Ex aluation Awas made of t-o particular forms of bias to which attention has recent1s been drawn (Hosek et al 1996;Weiss and Lazoxich. 1996).…”

Benefit of screening mammography in reducing the rate of late-stage breast cancer diagnoses (United States)

“…To determine whether our results were unduly influenced by our decision to study mammograms in the 2 years prior to the reference date [25], we repeated the analyses with lookback periods of To determine whether including the screening mammogram that led to the diagnosis of late-stage Table 3a. If Hosek's argument holds, the true association should lie between the two estimates [26]. For women aged 40 or 41 at the reference date, our 2-year lookback captured screening mammograms at ages 38 or 39, before the recommended age to begin screening.…”

Outcomes of surveillance mammography after treatment of primary breast cancer: a population-based case series

“…These biases also apply to our previously used method of annual conditional survival cohorts, and have dissuaded us from operationalizing SM as a time dependent covariate. We have also described the frequency of detection of CRICB and CPBC by SM, but after careful consideration of biases associated with detection (lead time and length bias), we have not included detection in analysis [14][15][16][17][18][19][20][21].…”