Researchers conducted a meta-analysis on the relationship between Z and X, and found a summary effect size of -0.08, p 0.05, even though all of the individual effect sizes were highly significant. What could be potential reasons for this observed summary effect size?
A) they may have included too few primary studies in their meta-analysis, and thus their meta-analysis is underpowered
B) the distribution of effect sizes if very heterogeneous, with positive and negative individual effect sizes cancelling each other out
C) there may be an important moderator that is masking the true relationship between Z and X
D) A and B
E) B and C
F) all of the above

Question

Researchers conducted a meta-analysis on the relationship between Z and X, and found a summary effect size of -0.08, p > 0.05, even though all of the individual effect sizes were highly significant. What could be potential reasons for this observed summary effect size?
A) they may have included too few primary studies in their meta-analysis, and thus their meta-analysis is underpowered
B) the distribution of effect sizes if very heterogeneous, with positive and negative individual effect sizes cancelling each other out
C) there may be an important moderator that is masking the true relationship between Z and X
D) A and B
E) B and C
F) all of the above

Quizplus · Accepted Answer

The observed summary effect size of -0.08 with p > 0.05 in the meta-analysis, despite highly significant individual effect sizes, could be due to several factors. Including too few primary studies could result in an underpowered meta-analysis (A). If the distribution of effect sizes is very heterogeneous, with some studies showing positive effects and others showing negative effects, these could cancel each other out, leading to a small summary effect size (B). Additionally, the presence of an important moderator that affects the relationship between Z and X could be masking the true effect, making it appear weaker or non-significant in the meta-analysis (C). Therefore, all of the provided reasons (A, B, and C) could potentially explain the observed summary effect size.

Researchers Conducted a Meta-Analysis on the Relationship Between Z and X