title: Participant blinding and gastrointestinal illness in a randomized, controlled trial of an in-home drinking water intervention.
abstract: 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.affiliation: School of Public Health, University of California-Berkeley, 140 Warren Hall #7360, Berkeley, CA 94720, USA. jcolford@socrates.berkeley.edu
authors.forename: John M
authors.initials: JM
authors.lastname: Colford
authors.forename: Judy R
authors.initials: JR
authors.lastname: Rees
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Wade
authors.forename: Asheena
authors.initials: A
authors.lastname: Khalakdina
authors.forename: Joan F
authors.initials: JF
authors.lastname: Hilton
authors.forename: Isaac J
authors.initials: IJ
authors.lastname: Ergas
authors.forename: Susan
authors.initials: S
authors.lastname: Burns
authors.forename: Anne
authors.initials: A
authors.lastname: Benker
authors.forename: Catherine
authors.initials: C
authors.lastname: Ma
authors.forename: Cliff
authors.initials: C
authors.lastname: Bowen
authors.forename: Daniel C
authors.initials: DC
authors.lastname: Mills
authors.forename: Duc J
authors.initials: DJ
authors.lastname: Vugia
authors.forename: Dennis D
authors.initials: DD
authors.lastname: Juranek
authors.forename: Deborah A
authors.initials: DA
authors.lastname: Levy
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002140:California; D002648:Child; D004311:Double-Blind Method; D004326:Drinking; D005240:Feasibility Studies; D005260:Female; D005767:Gastrointestinal Diseases / Q000175:diagnosis / Q000209:etiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010865:Pilot Projects; D011786:Quality Control; D011795:Surveys and Questionnaires; D018508:Water Purification / Q000592:standards*; D014881:Water Supply