The systematic review carried out by Taylor et al1 suggested that selective serotonin reuptake inhibitors (SSRIs) begin to have observable beneficial effects in depression during the first week of treatment. This result was obtained from the analysis of randomized controlled trials of SSRIs vs placebo that reported outcomes for at least 2 points in the first 4 weeks of treatment. From 107 trial reports, Taylor et al identified 50 randomized controlled trials meeting the inclusion criteria, of which 28 were incorporated in the primary analysis. This pattern of trial selection was a consequence of the fact that not all studies took repeated-outcome measures and not all studies that took repeated-outcome measures presented the results for all points.
Barbui C, Cipriani A. Publication Bias in Systematic Reviews. Arch Gen Psychiatry. 2007;64(7):868. doi:10.1001/archpsyc.64.7.868-a