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.
Colford
John M
JM
School of Public Health, University of California-Berkeley, 140 Warren Hall #7360, Berkeley, CA 94720, USA. jcolford@socrates.berkeley.edu
Rees
Judy R
JR
Wade
Timothy J
TJ
Khalakdina
Asheena
A
Hilton
Joan F
JF
Ergas
Isaac J
IJ
Burns
Susan
S
Benker
Anne
A
Ma
Catherine
C
Bowen
Cliff
C
Mills
Daniel C
DC
Vugia
Duc J
DJ
Juranek
Dennis D
DD
Levy
Deborah A
DA
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