Figure 4.

Contour-enhanced funnel plot including published studies suggests publication bias. The white area and the region on its left side contain studies with statistically non-significant amnestic effects based on one-tailed tests (drug < control; p ≥ 0.05). The plot suggests that non-significant studies are missing in the literature (i.e., publication bias). Remarkably, effect sizes are most densely plotted at the border of statistical significance, which might also imply biased effect sizes.