Statistical issues in a metaregression analysis of randomized trials: Impact on the dietary sodium intake and blood pressure relationship

In a meta-analysis of randomized trials of the effects of dietary sodium in terventions on blood pressure, we found substantial heterogeneity among the studies. We were interested in evaluating whether measurement error, known to be a problem for dietary sodium measures, publication bias, or confound ing factors could be responsible for the heterogeneity. A measurement error correction was developed that corrects both the slope and the intercept an d takes into account the sample size of each study and the number of measur ements taken on an individual. The measurement error correction had a minim al effect on the estimates, although it performed well in simulated data. A smoothed scatter plot was used to assess publication bias. Metaregressions provide a convenient way to jointly assess the effects of several factors, but care must be taken to fit an appropriate model.