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Bounding the per-protocol effect in randomized trials: an application to colorectal cancer screening.

ABSTRACT: BACKGROUND:The per-protocol effect is the effect that would have been observed in a randomized trial had everybody followed the protocol. Though obtaining a valid point estimate for the per-protocol effect requires assumptions that are unverifiable and often implausible, lower and upper bounds for the per-protocol effect may be estimated under more plausible assumptions. Strategies for obtaining bounds, known as "partial identification" methods, are especially promising in randomized trials. RESULTS:We estimated bounds for the per-protocol effect of colorectal cancer screening in the Norwegian Colorectal Cancer Prevention trial, a randomized trial of one-time sigmoidoscopy screening in 98,792 men and women aged 50-64 years. The screening was not available to the control arm, while approximately two thirds of individuals in the treatment arm attended the screening. Study outcomes included colorectal cancer incidence and mortality over 10 years of follow-up. Without any assumptions, the data alone provide little information about the size of the effect. Under the assumption that randomization had no effect on the outcome except through screening, a point estimate for the risk under no screening and bounds for the risk under screening are achievable. Thus, the 10-year risk difference for colorectal cancer was estimated to be at least -0.6 % but less than 37.0 %. Bounds for the risk difference for colorectal cancer mortality (-0.2 to 37.4 %) and all-cause mortality (-5.1 to 32.6 %) had similar widths. These bounds appear helpful in quantifying the maximum possible effectiveness, but cannot rule out harm. By making further assumptions about the effect in the subpopulation who would not attend screening regardless of their randomization arm, narrower bounds can be achieved. CONCLUSIONS:Bounding the per-protocol effect under several sets of assumptions illuminates our reliance on unverifiable assumptions, highlights the range of effect sizes we are most confident in, and can sometimes demonstrate whether to expect certain subpopulations to receive more benefit or harm than others. TRIAL REGISTRATION:Clinicaltrials.gov identifier NCT00119912 (registered 6 July 2005).

SUBMITTER: Swanson SA

PROVIDER: S-EPMC4666083 | biostudies-literature | 2015 Nov

REPOSITORIES: biostudies-literature

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Bounding the per-protocol effect in randomized trials: an application to colorectal cancer screening.

Swanson Sonja A SA Holme Øyvind Ø Løberg Magnus M Kalager Mette M Bretthauer Michael M Hoff Geir G Aas Eline E Hernán Miguel A MA

Trials 20151130

<h4>Background</h4>The per-protocol effect is the effect that would have been observed in a randomized trial had everybody followed the protocol. Though obtaining a valid point estimate for the per-protocol effect requires assumptions that are unverifiable and often implausible, lower and upper bounds for the per-protocol effect may be estimated under more plausible assumptions. Strategies for obtaining bounds, known as "partial identification" methods, are especially promising in randomized tri ...[more]

PMID: 26620120

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Project description:ImportanceColorectal cancer (CRC) screening is underused in the US. Tailored message interventions have shown benefit for increasing screening uptake of mammography and Papanicolaou testing, but their role in CRC screening is less clear.ObjectiveTo evaluate the effectiveness of a tailored message telephone intervention prior to scheduling of a screening or surveillance colonoscopy and its effect on CRC screening completion rates.Design, setting, and participantsThis randomized clinical trial was conducted from July 2017 through August 2018 at the University of Pennsylvania Health System (UPHS), an urban academic medical center. Participants were asymptomatic patients aged 50 to 75 years who were eligible for CRC screening or surveillance, had been referred for colonoscopy, and did not have a scheduled colonoscopy appointment. Data analysis was conducted from January to September 2019.InterventionsPatients underwent block randomization in a 1:1:1 ratio to 1 of 3 study arms. Participants in the usual care group were contacted via a mailed letter and instructed to call to schedule a colonoscopy. In the generic message group, participants were contacted by telephone, completed an assessment, and received a uniform, nontailored message encouraging colonoscopy scheduling. Participants in the tailored message group were contacted by telephone, completed an assessment, and received a tailored message encouraging colonoscopy scheduling based on their identified assessment cohort.Main outcomes and measuresThe primary outcome was colonoscopy completion rate within 120 days of enrollment. The secondary outcome was colonoscopy scheduling rate appointment within 120 days of enrollment.ResultsA total of 600 participants (median [IQR] age, 56 [51-63] years; 373 women [62.2%]) were enrolled, including 200 participants randomized to usual care, 200 participants randomized to the generic message, and 200 participants randomized to the tailored message. The total sample included 12 Asian participants (2.0%), 324 Black participants (54.0%), and 227 White participants (37.8%), and 9 participants (1.5%) were of Latino or Hispanic ethnicity. Colonoscopy completion was significantly higher for both the tailored message group (69 participants [34.5%]) and the generic message group (64 participants [32.0%]) compared with the usual care group (37 participants [18.5%]) (P < .001 and P = .002, respectively). Scheduling rates were also significantly higher in both groups, with 106 participants (53.0%) in the tailored message group and 105 participants (52.5%) in the generic message group scheduling appointments, compared with 54 participants (27.0%) in the usual care arm (P < .001 for both).Conclusions and relevanceIn this randomized clinical trial among individuals whose CRC screening was not up to date, both a tailored message intervention and a generic message intervention were significantly more effective at increasing colonoscopy scheduling and completion rates compared with usual care. These findings suggest that individualized health communications can increase individual motivation to obtain CRC screening.Trial registrationClinicalTrials.gov Identifier: NCT03310892.

Project description:BackgroundRandomized controlled trials (RCTs) have yielded varying estimates of the benefit of flexible sigmoidoscopy (FS) screening for colorectal cancer (CRC). Our objective was to more precisely estimate the effect of FS-based screening on the incidence and mortality of CRC by performing a meta-analysis of published RCTs.Methods and findingsMedline and Embase databases were searched for eligible articles published between 1966 and 28 May 2012. After screening 3,319 citations and 29 potentially relevant articles, two reviewers identified five RCTs evaluating the effect of FS screening on the incidence and mortality of CRC. The reviewers independently extracted relevant data; discrepancies were resolved by consensus. The quality of included studies was assessed using criteria set out by the Evidence-Based Gastroenterology Steering Group. Random effects meta-analysis was performed. The five RCTs meeting eligibility criteria were determined to be of high methodologic quality and enrolled 416,159 total subjects. Four European studies compared FS to no screening and one study from the United States compared FS to usual care. By intention to treat analysis, FS-based screening was associated with an 18% relative risk reduction in the incidence of CRC (0.82, 95% CI 0.73-0.91, p<0.001, number needed to screen [NNS] to prevent one case of CRC = 361), a 33% reduction in the incidence of left-sided CRC (RR 0.67, 95% CI 0.59-0.76, p<0.001, NNS = 332), and a 28% reduction in the mortality of CRC (relative risk [RR] 0.72, 95% CI 0.65-0.80, p<0.001, NNS = 850). The efficacy estimate, the amount of benefit for those who actually adhered to the recommended treatment, suggested that FS screening reduced CRC incidence by 32% (p<0.001), and CRC-related mortality by 50% (p<0.001). Limitations of this meta-analysis include heterogeneity in the design of the included trials, absence of studies from Africa, Asia, or South America, and lack of studies comparing FS with colonoscopy or stool-based testing.ConclusionsThis meta-analysis of randomized controlled trials demonstrates that FS-based screening significantly reduces the incidence and mortality of colorectal cancer in average-risk patients.

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Bounding the per-protocol effect in randomized trials: an application to colorectal cancer screening.

Publications

Bounding the per-protocol effect in randomized trials: an application to colorectal cancer screening.

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