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Selection effects and prevention program outcomes.

ABSTRACT: A primary goal of the paper is to provide an example of an evaluation design and analytic method that can be used to strengthen causal inference in nonexperimental prevention research. We used this method in a nonexperimental multisite study to evaluate short-term outcomes of a preventive intervention, and we accounted for effects of two types of selection bias: self-selection into the program and differential dropout. To provide context for our analytic approach, we present an overview of the counterfactual model (also known as Rubin's causal model or the potential outcomes model) and several methods derived from that model, including propensity score matching, the Heckman two-step approach, and full information maximum likelihood based on a bivariate probit model and its trivariate generalization. We provide an example using evaluation data from a community-based family intervention and a nonexperimental control group constructed from the Washington State biennial Healthy Youth Survey (HYS) risk behavior data (HYS n?=?68,846; intervention n?=?1,502). We identified significant effects of participant, program, and community attributes in self-selection into the program and program completion. Identification of specific selection effects is useful for developing recruitment and retention strategies, and failure to identify selection may lead to inaccurate estimation of outcomes and their public health impact. Counterfactual models allow us to evaluate interventions in uncontrolled settings and still maintain some confidence in the internal validity of our inferences; their application holds great promise for the field of prevention science as we scale up to community dissemination of preventive interventions.

SUBMITTER: Hill LG

PROVIDER: S-EPMC3760982 | biostudies-literature | 2013 Dec

REPOSITORIES: biostudies-literature

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Selection effects and prevention program outcomes.

Hill Laura G LG Rosenman Robert R Tennekoon Vidhura V Mandal Bidisha B

Prevention science : the official journal of the Society for Prevention Research 20131201 6

A primary goal of the paper is to provide an example of an evaluation design and analytic method that can be used to strengthen causal inference in nonexperimental prevention research. We used this method in a nonexperimental multisite study to evaluate short-term outcomes of a preventive intervention, and we accounted for effects of two types of selection bias: self-selection into the program and differential dropout. To provide context for our analytic approach, we present an overview of the c ...[more]

PMID: 23417667

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Project description:The largest and longest clinical trial of metformin for the prevention of diabetes is the Diabetes Prevention Program/Diabetes Prevention Program Outcomes Study (DPP/DPPOS). In this review, we summarise data from the DPP/DPPOS, focusing on metformin for diabetes prevention, as well as its long-term glycaemic and cardiometabolic effects and safety in people at high-risk of developing diabetes. The DPP (1996-2001) was a RCT of 3234 adults who, at baseline, were at high-risk of developing diabetes. Participants were assigned to masked placebo (n = 1082) or metformin (n = 1073) 850 mg twice daily, or intensive lifestyle intervention (n = 1079). The masked metformin/placebo intervention phase ended approximately 1 year ahead of schedule because of demonstrated efficacy. Primary outcome was reported at 2.8 years. At the end of the DPP, all participants were offered lifestyle education and 88% (n = 2776) of the surviving DPP cohort continued follow-up in the DPPOS. Participants originally assigned to metformin continued to receive metformin, unmasked. The DPP/DPPOS cohort has now been followed for over 15 years with prospective assessment of glycaemic, cardiometabolic, health economic and safety outcomes. After an average follow-up of 2.8 years, metformin reduced the incidence of diabetes by 31% compared with placebo, with a greater effect in those who were more obese, had a higher fasting glucose or a history of gestational diabetes. The DPPOS addressed the longer-term effects of metformin, showing a risk reduction of 18% over 10 and 15 years post-randomisation. Metformin treatment for diabetes prevention was estimated to be cost-saving. At 15 years, lack of progression to diabetes was associated with a 28% lower risk of microvascular complications across treatment arms, a reduction that was no different among treatment groups. Recent findings suggest metformin may reduce atherosclerosis development in men. Originally used for the treatment of type 2 diabetes, metformin, now proven to prevent or delay diabetes, may serve as an important tool in battling the growing diabetes epidemic. Long-term follow-up, currently underway in the DPP/DPPOS, is now evaluating metformin's potential role, when started early in the spectrum of dysglycaemia, on later-stage comorbidities, including cardiovascular disease and cancer.Trial registrationClinicalTrials.gov NCT00038727 and NCT00004992.

Project description:BackgroundThe Diabetes Prevention Program (DPP) was a randomized, controlled clinical trial. It demonstrated that among high-risk individuals with impaired glucose tolerance, diabetes incidence was reduced by 58 % with lifestyle intervention and 31 % with metformin compared to placebo. During the Diabetes Prevention Program Outcomes Study (DPPOS), all DPP participants were unmasked to their treatment assignments, the original lifestyle intervention group was offered additional lifestyle support, the metformin group continued metformin, and all three groups were offered a group-implemented lifestyle intervention. Over the 10 years of combined DPP/DPPOS follow-up, diabetes incidence was reduced by 34 % in the lifestyle group and 18 % in the metformin group compared to placebo. The purpose of this article is to review and synthesize analyses published by the DPP/DPPOS Research Group that have described the cost-effectiveness of diabetes prevention.MethodsWe describe the resource utilization and costs of the DPP and DPPOS interventions, the costs of non-intervention-related medical care, the impact of the interventions on diabetes progression and quality-of-life, and the cost-effectiveness of the interventions from health system and societal perspectives. Cost-effectiveness analyses were performed with a 3-year time horizon using DPP data, a lifetime time horizon that simulated 3-year DPP data, and a 10-year time horizon using combined DPP/DPPOS data.ResultsAlthough more expensive than the placebo intervention, the greater costs of the lifestyle and metformin interventions were offset by reductions in the costs of nonintervention-related medical care. Every year after randomization, quality-of-life was better for participants in the lifestyle intervention compared to those in the metformin or placebo intervention. In both the simulated lifetime analysis and the 10-year within trial economic analysis, lifestyle and metformin were extremely cost-effective (that is, improved outcomes at a low incremental cost) or even cost-saving (that is, improved outcomes and reduced total costs) compared to the placebo intervention.ConclusionsThe implementation of diabetes prevention programs in high-risk individuals will result in important health benefits and represents a good value for money.Trial registrationNCT00004992 (DPP) and NCT00038727 (DPPOS).

Project description:To investigate long-term metformin adherence in the Diabetes Prevention Program Outcomes Study (DPPOS) by examining: (1) predictors of long-term adherence to study metformin and (2) whether metformin adherence was associated with incident type 2 diabetes. DPPOS was an open-label continuation of the randomized clinical trial (Diabetes Prevention Program (DPP)) in which eligible participants randomized to the metformin group were offered study metformin and followed over 11 years. A brief structured adherence interview was administered semiannually. Metformin adherence was assessed by pill counts. Predictors of metformin adherence were examined in multivariate regression models. Incident diabetes associated with metformin adherence and other variables was assessed in Cox proportional hazards models. Of 868 participants eligible to continue taking study metformin, 664 (76%) took at least some metformin over 11 years, with 478 of them reporting problems with adherence. DPPOS cumulative adherence showed significant associations of higher adherence (≥80%) with early adherence at 3 months in DPP (p<0.001) and lower depression scores during DPPOS (p<0.001); significant differences were also seen by race/ethnicity (p<0.004). Predicting adherence by multivariate modeling showed odds of adherence significantly lower for Black participants and for participants reporting more than one barrier. Odds for adherence were significantly higher for those adherent early in DPP and those reporting at least one planned strategy to improve adherence. Higher metformin adherence was significantly associated with a lower diabetes risk (p=0.04), even after adjustment for demographic variables, depression, and anxiety scores. In this long-term diabetes prevention study, early metformin adherence and planned strategies to promote adherence improved long-term adherence over 11 years; higher adherence to metformin was related to lower diabetes incidence. Incorporating strategies to promote adherence when initially prescribing metformin and counseling to support adherence over time are warranted.

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Selection effects and prevention program outcomes.

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Selection effects and prevention program outcomes.

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