Meta-analysis is useful because it

A) compares studies without the difficulties involved in statistical analysis.
B) statistically analyzes the results of many studies.
C) is simpler to use than previous methods of analyzing aggregate data.
D) ensures objective analysis of the results of multiple studies.

Meta-analysis is a statistical analysis that combines the results of multiple studies on a particular topic. This helps to increase the sample size and statistical power, reduce bias, and provide a more accurate estimate of the effect size. Therefore, option B is the correct choice. Option A is incorrect because meta-analysis also involves statistical analysis. Option C is incorrect because meta-analysis may involve complex statistical methods. Option D is incorrect because the objectivity of a meta-analysis depends on the quality of the individual studies included in the analysis.