Related Experiment Videos
Differences in endpoints between the Swedish W-E (two county) trial of mammographic screening and the Swedish
L Holmberg1, S W Duffy, A M F Yen
1Research Oncology, 3rd floor Bermondsey Wing, Guy's Hospital, Divison of Cancer Studies, Guy's Campus, King's College London, SE1 9RT London, UK. Lars.holmberg@kcl.ac.uk
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 W and 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.
Related Concept Videos
Bias in Epidemiological Studies
Types of Biopharmaceutical Studies: Controlled and Non-Controlled Approaches
Non-controlled studies, commonly employed for initial exploration, lack a control group, rendering them susceptible to biases and external influences. In contrast, controlled...
Effects of EDTA on End-Point Detection Methods
In the visual method, metal-ion indicators (metallochromic dyes), which have distinct colors in their free and complex forms, are added to the mixture to signal the titration's end point. They form stable complexes with metal ions, but these complexes are weaker than the corresponding metal–EDTA complexes. As a result, EDTA...
Comparing the Survival Analysis of Two or More Groups
Study Designs in Epidemiology
Observational studies are those where the researcher does not intervene but rather observes natural variations. They include cross-sectional, cohort, and case-control studies.
Bioequivalence studies: Biowaivers