Missing data are a common occurrence in survey-based research studies in education, and the way missing values are handled can significantly affect the results of analyses based on such data. Despite known problems with performance of some missing data handling methods, such as mean imputation, many researchers in education continue to use those…

In the context of reviewing an article for this journal (van der Linden & Sotaridona, this issue, pp. 283-304) the topic of unconditional and conditional hypothesis testing came under consideration. While this is hardly a new issue (consider, for example, arguments regarding the chi square vs. Fisher exact test of independence for a 2 x 2…

In meta-analysis, the usual way of assessing whether a set of single studies is homogeneous is by means of the Q test. However, the Q test only informs meta-analysts about the presence versus the absence of heterogeneity, but it does not report on the extent of such heterogeneity. Recently, the I[squared] index has been proposed to quantify the…

In policy research a frequent aim is to estimate treatment effects separately by subgroups. This endeavor becomes a methodological challenge when the subgroups are defined by post-treatment, rather than pre-treatment, variables because if analyses are performed in the same way as with pre-treatment variables, causal interpretations are no longer…