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

Multiple Choice

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