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Volume 8, Number 1—January 2002


Participant Blinding and Gastrointestinal Illness in a Randomized, Controlled Trial of an In-Home Drinking Water Intervention

John M. Colford*†Comments to Author , Judy R. Rees*†, Timothy J. Wade*†, Asheena Khalakdina*†, Joan F. Hilton‡, Isaac J. Ergas*, Susan Burns*, Anne Benker*, Catherine Ma, Cliff Bowen, Daniel C. Mills, Duc J. Vugia, Dennis D. Juranek¶, and Deborah A. Levy¶
Author affiliations: *University of California Berkeley, Berkeley, California, USA; †California Emerging Infections Program, Berkeley, California, USA; ‡University of California San Francisco, School of Medicine, San Francisco, California, USA §California Department of Health Services, Berkeley, California, USA; ¶Centers for Disease Control and Prevention, Atlanta, Georgia, USA;

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Table 2

Final (Week 16) Device Blinding Questionnaire, Pilot Water Evaluation Trial

Index respondents only
Guess Sham device group (%) Active device group (%) Total (%)
Sham 5 (16.1) 5 (15.2) 10 (15.6)
Active 13 (41.9) 19 (57.6) 32 (50.0)
Don’t know 13 (41.9) 9 (27.3) 22 (34.4)
Total 31 (100.0) 33 (100.0) 64 (100.0)

*Does not include 21 participants from the sham device group and 13 participants from the active device group who did not complete the final blinding questionnaire.

+Blinding index for all participants (adjusted for intrahousehold correlation, ρ=0.60)=0.64 (95% confidence interval [CI] 0.51–0.78). Blinding index for index respondents alone = 0.65 (95% CI 0.53–0.76).

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