Relation between XXXX mortality and screening effectiveness: systematic review of the mammography trials.

@entity5 @entity0
The mammography screening trials have shown varying results. This could be because screening was better in some trials than in others at advancing the time of diagnosis. If so, more @entity5 would be identified in such trials relative to the control group, and fewer of the @entity5 would have reached an advanced stage. I performed a systematic review of the mammography screening trials using metaregression. Finding many @entity5 was not related to the size of the reduction in @entity0 mortality (p = 0.19 after seven and p = 0.73 after 13 years of follow-up). In contrast, finding few @entity5 in stage II and above predicted a larger reduction in @entity0 mortality (p = 0.04 and p = 0.006). This expected association was also found for node-positive @entity5 (p = 0.008 and p = 0.04). However, a screening effectiveness of zero (same proportion of node-positive @entity5 in the screened group as in the control group) predicted a significant 16% reduction in @entity0 mortality after 13 years (95% confidence interval, 9% to 23% reduction). This can only occur if there is bias. Further analyses uncovered bias in both assessment of the cause of @entity5 in advanced stages. Consequently, the differences in the reported reductions in @entity0 mortality cannot be explained by differences in screening effectiveness. Given that the size of the bias was similar to the estimated screening effect, screening appeared ineffective.
