Figure 2.

Funnel plots to identify doubtful studies.

In these graphs, each study result is represented by a point function of gain for MD or CD (x axis) and of study precision (y axis). The average mean is represented by a vertical line. The surrounding curves represent the 95% CI, which reduces as precision is increased (higher population, smaller SE). Abnormally high effect sizes (CD) in contradiction with MD (as for Zhang), demonstrate the under-rating of SD and SE.

Note: 2 points below an author's name, describe 2 products (device and/or control)