Saturday, April 25, 2009
Fighting Confirmation Bias in Fish Oil
Ben Goldacre covers both one null result of fish oil's efficacy in children and explains how subgroup analysis in statistics can be used to mine for positive results when there are none in the main sample. He notes that in 1973, Lee et al randomly assigned patients to non-existent treatment groups. They were able to find a subgroup, characterized by odd disorders ("three-vennel disease" and "abnormal left ventricular contraction"), where Treatment 1 had a significantly higher survival rate than Treatment 2. So be wary when researchers report statistical significance in subgroups only, unless it is clearly a biologically relevant subgroup and/or the researchers explicitly hypothesize the differences in subgroups before the trial. I do have one question though. Can't you control for this selection bias with an ANOVA for main effects?