Psychometric evaluation of the Diabetes Symptom Checklist-Revised (DSC-R)--a measure of symptom distress.

OBJECTIVE: To assess the psychometric validity, reliability, responsiveness, and minimal important differences of the Diabetes Symptoms Checklist-Revised (DSC-R), a widely used patient-reported outcome measure of diabetes symptom distress. RESEARCH DESIGN AND METHODS: Psychometric validity of the DSC-R was assessed using blinded data from a large-scale trial of approximately 4000 type 2 diabetes patients. Confirmatory factorial analysis (CFA) and multitrait analysis were used to examine the construct validity of the structure of DSC-R. DSC-R internal consistency, discriminative validity, and responsiveness were also assessed. Distribution and anchor-based methods were used to estimate minimal important differences for DSC-R domains. RESULTS: Mean age of the sample was 56 years, 42% were female, 88% were Caucasian. Patients had a mean body mass index (BMI) of 32.2 and mean glucose-fasting level of 151.7 md/dl. CFA and multitrait analysis indicated that the scoring of the DSC-R has acceptable construct validity. Item-scale correlations ranged from 0.44 to 0.78. Cronbach's alpha coefficients ranged from 0.69 to 0.87. At baseline, DSC-R scores were higher among patients with higher BMI scores (P < 0.0001), supporting the discriminative validity of the DSC-R. Minimal important difference estimates ranged from 0.39 to 0.60 points when using distribution methods and from 0.00 to 0.33 when estimated using anchor-based methods. CONCLUSIONS: The DSC-R demonstrated excellent psychometric properties when tested in a large-scale diabetes clinical trial. Responsiveness and test-retest reliability of the DSC-R warrant further evaluation.

Costs of medication nonadherence in patients with diabetes mellitus: a systematic review and critical analysis of the literature.

OBJECTIVES: Information on the health care costs associated with nonadherence to treatments for diabetes is both limited and inconsistent. We reviewed and critically appraised the literature to identify the main methodological issues that might explain differences among reports in the relationship of nonadherence and costs in patients with diabetes. METHODS: Two investigators reviewed Medline, EMBASE, Cochrane library and CINAHL and studies with information on costs by level of adherence in patients with diabetes published between January 1, 1997 and September 30th 2007 were included. RESULTS: A total of 209 studies were identified and ten fulfilled the inclusion criteria. All included studies analyzed claims data and 70% were based on non-Medicaid and non-Medicare databases. Low medication possession ratios were associated with higher costs. Important differences were found in the ICD-9/ICD-9 CM codes used to identify patients and their diagnoses, data sources, analytic window period, definitions of adherence measures, skewness in cost data and associated statistical issues, adjustment of costs for inflation, adjustment for confounders, clinical outcomes and costs. CONCLUSIONS: Important variation among cost estimates was evident, even within studies of the same population. Readers should be cautious when comparing estimated coefficients from various studies because methodological issues might explain differences in the results of costs of nonadherence in diabetes. This is particularly important when estimates are used as inputs to pharmacoeconomic models.

Cost-effectiveness of atypical antipsychotics for the management of schizophrenia in the UK .

OBJECTIVE: To evaluate the cost-effectiveness of atypical antipsychotic treatment sequences for the management of stable schizophrenia in the UK. RESEARCH DESIGN AND METHODS: A Markov model was developed to assess the cost per quality-adjusted life year (QALY) gained from 12 alternative treatment sequences each containing two of four atypical antipsychotics (aripiprazole, olanzapine, quetiapine and risperidone), followed by clozapine. The main model parameters were populated with data from the Clinical Antipsychotic Trials of Intervention Effectiveness (CATIE) study and a recent trial comparing aripiprazole with olanzapine. Patients enter the model with stable schizophrenia and may relapse, discontinue or continue and experience adverse events (AEs), or develop diabetes. Population mortality was adjusted for schizophrenia and diabetes. Utility decrements applied to stable schizophrenia, relapse, diabetes and treatment-related AEs were taken from a direct UK utility elicitation study. Resource use and unit costs were taken from published sources. A time horizon of 10 years was adopted. Results are based on 10,000 probabilistic iterations of the model. RESULTS: Aripiprazole followed by risperidone produced the greatest number of QALYs, an additional 0.03 compared with risperidone followed by olanzapine, at an incremental cost of £257 (incremental cost/QALY: £9,440). Aripiprazole followed by risperidone had the greatest probability among evaluated sequences of being cost-effective at a threshold of >£10,000/QALY. All other strategies were dominated by at least one of these strategies. The impact of lower pricing for risperidone (based on generic availability) did not impact results. CONCLUSIONS: Modelling the cost-effectiveness of different treatment sequences for stable schizophrenia is appropriate given that patients rarely remain on one treatment for long periods. The treatment sequence aripiprazole followed by risperidone was the most cost-effective option for patients with stable schizophrenia in the UK.