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Participant blinding and gastrointestinal illness in a randomized, controlled trial of an in-home drinking water intervention.

We conducted a randomized, triple-blinded home drinking water intervention trial to determine if a large study could be undertaken while successfully blinding participants. Households were randomized 50:50 to use externally identical active or sham treatment devices. We measured the effectiveness of blinding of participants by using a published blinding index in which values >0.5 indicate successful blinding. The principal health outcome measured was “highly credible gastrointestinal illness” (HCGI). Participants (n=236) from 77 households were successfully blinded to their treatment assignment. At the end of the study, the blinding index was 0.64 (95% confidence interval 0.51-0.78). There were 103 episodes of HCGI during 10,790 person-days at risk in the sham group and 82 episodes during 11,380 person-days at risk in the active treatment group. The incidence rate ratio of disease (adjusted for the clustered sampling) was 1.32 (95% CI 0.75, 2.33) and the attributable risk was 0.24 (95% CI -0.33, 0.57). These data confirm that participants can be successfully blinded to treatment group assignment during a randomized trial of an in-home drinking water intervention.

Authors: Colford, John M Jr; Rees, Judy R; Wade, Timothy J; Khalakdina, Asheena; Hilton, Joan F; Ergas, Isaac J; Burns, Susan; Benker, Anne; Ma, Catherine; Bowen, Cliff; Mills, Daniel C; Vugia, Duc J; Juranek, Dennis D; Levy, Deborah A

Emerg Infect Dis. 2002 Jan;8(1):29-36.

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