Universität zu Köln

Stang, Andreas and Baethge, Christopher (2018). Imbalance p values for baseline covariates in randomized controlled trials: a last resort for the use of p values? A pro and contra debate. Clin. Epidemiol., 10. S. 531 - 536. ALBANY: DOVE MEDICAL PRESS LTD. ISSN 1179-1349

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Abstract

Background: Results of randomized controlled trials (RCTs) are usually accompanied by a table that compares covariates between the study groups at baseline. Sometimes, the investigators report p values for imbalanced covariates. The aim of this debate is to illustrate the pro and contra of the use of these p values in RCTs. Pro: Low p values can be a sign of biased or fraudulent randomization and can be used as a warning sign. They can be considered as a screening tool with low positive-predictive value. Low p values should prompt us to ask for the reasons and for potential consequences, especially in combination with hints of methodological problems. Contra: A fair randomization produces the expectation that the distribution of p values follows a flat distribution. It does not produce an expectation related to a single p value. The distribution of p values in RCTs can be influenced by the correlation among covariates, differential misclassification or differential mismeasurement of baseline covariates. Given only a small number of reported p values in the reports of RCTs, judging whether the realized p value distribution is, indeed, a flat distribution becomes difficult. If p values <= 0.005 or >= 0.995 were used as a sign of alarm, the false-positive rate would be 5.0% if randomization was done correctly, and five p values per RCT were reported. Conclusion: Use of a low p value as a warning sign that randomization is potentially biased can be considered a vague heuristic. The authors of this debate are obviously more or less enthusiastic with this heuristic and differ in the consequences they propose.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Stang, Andreas UNSPECIFIED UNSPECIFIED UNSPECIFIED Baethge, Christopher UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-202976
DOI:	10.2147/CLEP.S161508
Journal or Publication Title:	Clin. Epidemiol.
Volume:	10
Page Range:	S. 531 - 536
Date:	2018
Publisher:	DOVE MEDICAL PRESS LTD
Place of Publication:	ALBANY
ISSN:	1179-1349
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language Public, Environmental & Occupational Health Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/20297