Evidence map›Paper›PMID 27790968›Full record

ArticleEpidemiology and psychiatric sciences2017

Pre-post effect sizes should be avoided in meta-analyses.

P Cuijpers, E Weitz, I A Cristea, J Twisk

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PubMed Full text at PMC Publisher
In one paragraph

Article in Epidemiology and psychiatric sciences, 2017. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Cited by 155 papers, 108 of them syntheses that pooled it.

0numbers the graph read from it
0cells of the map it votes in
155citing papers in PubMed, 108 pooled it
–field-weighted citation impact
1 · What the graph read from it

What it found

Each row is one number read from the abstract, on the scale the paper reported it, with its interval. Left of the dashed line favours the treatment, right favours the comparator. Under each row is the sentence it came from. New to these charts? A ten-minute tutorial.

The abstract states no effect estimate the extractor could read, or names no intervention and outcome on the map, so this paper lights no cell and moves no belief. It is still indexed, cited and linked below.

2 · The registry

The trial behind it

Trials whose registry record cites this paper, or whose number appears in the abstract. A trial that started after this paper was published is citing it as background, not reporting it.

Neither the registry nor the abstract names a trial number. If this is a trial report, that itself is worth knowing.

3 · Its place in the literature

Who cites it

155 citing papers in PubMed, 108 syntheses or guidelines pooled it.

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  5. Emotion-Related Treatments in Patients With Binge Eating Episodes-a Systematic Review and Meta-Analysis.Obesity reviews : an official journal of the International Association for the Study of Obesity · 2026
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  10. Health-related quality of life in patients receiving medicinal cannabis: systematic review and meta-analysis of primary research findings 2015-2025.Quality of life research : an international journal of quality of life aspects of treatment, care and rehabilitation · 2026
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  19. Psychiatric and Cognitive Functioning After Metabolic and Bariatric Surgery: A Systematic Review and Meta-Analysis.Obesity reviews : an official journal of the International Association for the Study of Obesity · 2025
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  20. Tofersen for SOD1 amyotrophic lateral sclerosis: a systematic review and meta-analysis.Neurological sciences : official journal of the Italian Neurological Society and of the Italian Society of Clinical Neurophysiology · 2025
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95 more citing papers are in PubMed but not listed here.

4 · The record

Corrections and comments

PubMed lists nothing against this paper. Absence here is not a guarantee, only a check that was made.

5 · Who and what money

Authors and funding

4 authors.

P CuijpersDepartment of Clinical, Neuro and Developmental Psychology,Vrije Universiteit Amsterdam,The Netherlands.
E WeitzDepartment of Clinical, Neuro and Developmental Psychology,Vrije Universiteit Amsterdam,The Netherlands.
I A CristeaDepartment of Clinical Psychology and Psychotherapy,Babes-Bolyai University,Cluj-Napoca,Romania.
J TwiskEMGO Institute for Health and Care Research,The Netherlands.

Funding

No grant is acknowledged in the PubMed record.

6 · The paper itself

Abstract

Aims The standardised mean difference (SMD) is one of the most used effect sizes to indicate the effects of treatments. It indicates the difference between a treatment and comparison group after treatment has ended, in terms of standard deviations. Some meta-analyses, including several highly cited and influential ones, use the pre-post SMD, indicating the difference between baseline and post-test within one (treatment group).

methodsIn this paper, we argue that these pre-post SMDs should be avoided in meta-analyses and we describe the arguments why pre-post SMDs can result in biased outcomes.

resultsOne important reason why pre-post SMDs should be avoided is that the scores on baseline and post-test are not independent of each other. The value for the correlation should be used in the calculation of the SMD, while this value is typically not known. We used data from an 'individual patient data' meta-analysis of trials comparing cognitive behaviour therapy and anti-depressive medication, to show that this problem can lead to considerable errors in the estimation of the SMDs. Another even more important reason why pre-post SMDs should be avoided in meta-analyses is that they are influenced by natural processes and characteristics of the patients and settings, and these cannot be discerned from the effects of the intervention. Between-group SMDs are much better because they control for such variables and these variables only affect the between group SMD when they are related to the effects of the intervention.

conclusionsWe conclude that pre-post SMDs should be avoided in meta-analyses as using them probably results in biased outcomes.

Indexed as

Meta-Analysis as TopicReference StandardsAntidepressive AgentsCognitive Behavioral TherapyDepressionHumansAntidepressive AgentsIndividual patient datameta-analysespre-post effect sizesstandardised mean difference

Identifiers

PMID27790968
PMCPMC6998624

What OpenQuestion holds

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Registered trials

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Read under generation 80e0d062 · epoch 390. Bibliography from PubMed, PubMed Central and OpenAlex; grants from NIH RePORTER; trial links from ClinicalTrials.gov; estimates, votes and beliefs from the OpenQuestion graph.