16 The outcome of interest is clinical improvement and risk ratios (RRs) larger than 1 favour haloperidol over placebo. This dataset has been previously used to evaluate the impact of missing data on clinical outcomes 15 and is originally based on a Cochrane review. 14Īs a working example, we use a systematic review that comprises 17 trials comparing haloperidol and placebo for the treatment of symptoms in schizophrenia.
We employ different approaches and tools to assess whether publication bias is likely to operate using the commands metafunnel, 11 confunnel, 12 metatrim 13 and metabias. We use the metamiss command 10 to explore the impact of different assumptions about the mechanism of missing data on the summary effect. We provide an example of fixed and random effects meta-analysis using the metan command. 7 Failure to account for the unpublished studies may lead to biased summary estimates in favour of one of the two competing treatments (ie, usually the active or the newer intervention). 4 Publication bias occurs when publication of research results depends on their nature and direction. To explore and account for publication bias and small-study effects. Participants with missing outcome data may affect both the precision and the magnitude of the meta-analytic summary effect the latter can occur when the probability of missingness is related to the effectiveness of the interventions being compared 5 Prior to carrying out the statistical analyses, meta-analysts should consider the appropriate model (either fixed or random effects) for the specific clinical setting and outcomes of interest and then interpret the result under the light of the magnitude of the between-studies variability (heterogeneity) 3, 6
To conduct a fixed or a random effects meta-analysis. More specifically, in this paper we present Stata commands: 2 The theoretical and conceptual considerations of the methods we implement have been covered in recently published articles 3–5 and we suggest using these papers as companions when reading this manuscript. In this paper we focus on the statistical considerations involved in the meta-analysis process and we analyse an example from mental health in Stata.
1 The validity of the findings from a meta-analysis depends on several factors, such as the completeness of the systematic review, the plausibility of the assumptions made, the risk of bias in the individual studies and the potential for reporting biases. Systematic reviews and meta-analyses are often considered a reliable source of evidence to inform decisions about the effectiveness and safety of competing interventions.
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