Selection bias and subject refusal in a cluster-randomized controlled trial.

Autor: Yang R; Department of Pharmacy Practice & Science, College of Pharmacy, University of Iowa, Iowa City, IA, 52242, USA., Carter BL; Department of Pharmacy Practice & Science, College of Pharmacy, University of Iowa, Iowa City, IA, 52242, USA. barry-carter@uiowa.edu.; Department of Family Medicine, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, IA, USA. barry-carter@uiowa.edu., Gums TH; Department of Health Outcomes and Pharmacy Practice, University of Texas, Austin, TX, USA., Gryzlak BM; Department of Epidemiology, College of Public Health, University of Iowa, Iowa City, IA, USA., Xu Y; Department of Family Medicine, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, IA, USA., Levy BT; Department of Family Medicine, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, IA, USA.; Department of Epidemiology, College of Public Health, University of Iowa, Iowa City, IA, USA.
Jazyk: angličtina
Zdroj: BMC medical research methodology [BMC Med Res Methodol] 2017 Jul 10; Vol. 17 (1), pp. 94. Date of Electronic Publication: 2017 Jul 10.
DOI: 10.1186/s12874-017-0368-7
Abstrakt: Background: Selection bias and non-participation bias are major methodological concerns which impact external validity. Cluster-randomized controlled trials are especially prone to selection bias as it is impractical to blind clusters to their allocation into intervention or control. This study assessed the impact of selection bias in a large cluster-randomized controlled trial.
Methods: The Improved Cardiovascular Risk Reduction to Enhance Rural Primary Care (ICARE) study examined the impact of a remote pharmacist-led intervention in twelve medical offices. To assess eligibility, a standardized form containing patient demographics and medical information was completed for each screened patient. Eligible patients were approached by the study coordinator for recruitment. Both the study coordinator and the patient were aware of the site's allocation prior to consent. Patients who consented or declined to participate were compared across control and intervention arms for differing characteristics. Statistical significance was determined using a two-tailed, equal variance t-test and a chi-square test with adjusted Bonferroni p-values. Results were adjusted for random cluster variation.
Results: There were 2749 completed screening forms returned to research staff with 461 subjects who had either consented or declined participation. Patients with poorly controlled diabetes were found to be significantly more likely to decline participation in intervention sites compared to those in control sites. A higher mean diastolic blood pressure was seen in patients with uncontrolled hypertension who declined in the control sites compared to those who declined in the intervention sites. However, these findings were no longer significant after adjustment for random variation among the sites. After this adjustment, females were now found to be significantly more likely to consent than males (odds ratio = 1.41; 95% confidence interval = 1.03, 1.92).
Conclusions: Though there appeared to be a higher consent rate for females than for males, the overall impact of potential selection bias and refusal to participate was minimal. Without rigorous methodology, selection bias may be a threat to external validity in cluster-randomized trials.
Trial Registration: NCT01983813 . Date of registration: Oct. 28, 2013.
Databáze: MEDLINE
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