Document Detail

The effect of omitted covariates on confidence interval and study power in binary outcome analysis: a simulation study.
MedLine Citation:
PMID:  17011835     Owner:  NLM     Status:  MEDLINE    
BACKGROUND/OBJECTIVES: The consequence of omitted but balanced covariates on odds ratio point estimation is well-known in the literature. When exposure or intervention has a non-null effect on disease outcome, omitted covariates lead to underestimation of the effect of exposure or intervention. However, the effect of omitted covariates on confidence interval and study power is unknown. STUDY DESIGN AND SETTING: A simulation study is carried out to assess the effect of omitted covariates on confidence interval and study power for a plausible range of scenarios. Coverage probability and study power are assessed systematically over a range of study size, type of omitted covariate and magnitude of effect. A real-life example using a randomised experiment on flies' sexuality is provided. RESULTS: When a balanced covariate is omitted, coverage probability was lowered by 2.9-80%. Likewise study power was reduced by as much as 58%. The impact becomes substantial when the covariate is continuous, has large variability and has a larger effect than the effect of exposure or intervention. The result from a real-life example concurs with the simulation finding. CONCLUSION: Omitting an important balanced covariate lowers both coverage probability and study power. This implies the need for thoughtful consideration of important covariates at the design as well as the analysis stages of a study.
Abdissa Negassa; James A Hanley
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Publication Detail:
Type:  Journal Article     Date:  2006-08-23
Journal Detail:
Title:  Contemporary clinical trials     Volume:  28     ISSN:  1551-7144     ISO Abbreviation:  -     Publication Date:  2007 May 
Date Detail:
Created Date:  2007-03-05     Completed Date:  2007-05-11     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  101242342     Medline TA:  Contemp Clin Trials     Country:  United States    
Other Details:
Languages:  eng     Pagination:  242-8     Citation Subset:  IM    
Department of Epidemiology and Population Health, Division of Biostatistics, Albert Einstein College of Medicine of Yeshiva University, Bronx, NY, USA.
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MeSH Terms
Confidence Intervals*
Confounding Factors (Epidemiology)*
Models, Statistical*
Odds Ratio
Sexual Behavior, Animal

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