If a researcher performs a meta-analysis and finds that the mean d = 0.45, and the 95 percent confidence interval around this mean is (0.34, 0.56), what can the researcher conclude?
A) All future studies of this effect will find effect sizes somewhere between 0.34 and 0.56.
B) Averaging across all of the literature, there really is no effect.
C) There is a medium effect, but it is unclear what the direction of the effect is.
D) Averaging across all of the literature, there is a medium effect, and this effect is statistically significant.

Question

Quizplus · Accepted Answer

The best choice is D because the meta-analysis found a medium effect size of d=0.45, and the 95% confidence interval around this mean does not include zero. This means there is a statistically significant effect and it is medium in size. Therefore, we can conclude that averaging across all of the literature, there is a medium effect, and this effect is statistically significant. Choice A is incorrect because the 95% CI does not imply that all future effect sizes will fall within this range. Choice B is incorrect because the mean effect size is d=0.45, which is not zero. Choice C is incorrect because we know the direction of the effect is positive (since the CI only includes positive values).

If a Researcher Performs a Meta-Analysis and Finds That the Mean