1st approach to risk of bias

Research Question: Does screening women using mammograms prevent death from breast cancer?

Systematic review #1: Is Screening for Breast Cancer with Mammography Justifiable?

Risk of bias assessment: In 1999, a team of systematic reviewers decided that six of the eight identified studies on mammography had a “high” risk of bias. Briefly, the systematic reviewers were concerned that, in those six studies, the women who got mammograms were substantially different from the women who didn’t get mammograms. So, the researchers did not feel comfortable making a comparison between the two groups of women.

Because of this risk of bias, the researchers only considered the results from the remaining two studies.

Systematic review conclusion: Based on those two studies, it appeared that screening women using mammograms DOES NOT prevent deaths from breast cancer. The systematic reviewers concluded that mammograms are not worth the effort.

Five years later, another set of systematic reviewers took a different approach.