Mental health before and during the COVID-19 pandemic: a longitudinal probability sample survey of the UK population

This article describes the new meta-analysis command metaan, which can be used to perform fixed-or random-effects meta-analysis. Besides the standard DerSimonian and Laird approach, metaan offers a wide choice of available models: maximum likelihood, profile likelihood, restricted maximum likelihood, and a permutation model. The command reports a variety of heterogeneity measures, including Cochran's Q, I 2 , H 2 M , and the between-studies variance estimate b τ 2 . A forest plot and a graph of the maximum likelihood function can also be generated.

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Meta-analysis is a statistical methodology that combines or integrates the results of several independent clinical trials considered by the analyst to be 'combinable ' (Huque 1988). However, completeness and user-friendliness are uncommon both in specialised meta-analysis software packages and in mainstream statistical packages that have to rely on user-written commands. We implemented the meta-analysis methodology in an Microsoft Excel add-in which is freely available and incorporates more meta-analysis models (including the iterative maximum likelihood and profile likelihood) than are usually available, while paying particular attention to the user-friendliness of the package.