LAUSR

Background For outcomes that studies report as the means in the treatment and control groups, some medical applications and nearly half of meta-analyses in ecology express the effect as the ratio of means (RoM), also called the response ratio (RR), analyzed in the logarithmic scale as the log-response-ratio, LRR. Methods In random-effects meta-analysis of LRR, with normal and lognormal data, we studied the performance of estimators of the between-study variance, τ 2 , (measured by bias and coverage) in assessing heterogeneity of study-level effects, and also the performance of related estimators of the overall effect in the log scale, λ . We obtained additional empirical evidence from two examples. Results The results of our extensive simulations showed several challenges in using LRR as an effect measure. Point estimators of τ 2 had considerable bias or were unreliable, and interval estimators of τ 2 seldom had the intended 95% coverage for small to moderate-sized samples ( n <40). Results for estimating λ differed between lognormal and normal data. Conclusions For lognormal data, we can recommend only SSW, a weighted average in which a study’s weight is proportional to its effective sample size, (when n ≥40) and its companion interval (when n ≥10). Normal data posed greater challenges. When the means were far enough from 0 (more than one standard deviation, 4 in our simulations), SSW was practically unbiased, and its companion interval was the only option.