John R. Penrod

A Canadian, multicentre, randomized clinical trial of home-based pulmonary rehabilitation in chronic obstructive pulmonary disease: rationale and methods.

BACKGROUND Pulmonary rehabilitation remains largely underused. Self-monitored, home-based rehabilitation is a promising approach to improving the availability of pulmonary rehabilitation. OBJECTIVE To report the rationale and methods of a trial comparing the effectiveness of self-monitored, home-based rehabilitation with hospital-based, outpatient rehabilitation in patients with chronic obstructive pulmonary disease (COPD). STUDY DESIGN A parallel-group, randomized, noninferiority, multicentre trial will be performed with 240 patients with moderate to severe COPD. INTERVENTION Patients will be randomly assigned to conventional, supervised, hospital-based outpatient rehabilitation or self-monitored, home-based rehabilitation. Both interventions will include a standardized, comprehensive self-management program, in addition to the hospital-based outpatient or home-based exercise program. After the three-month intervention, patients in both groups will be encouraged to continue exercising at home. Patients will be assessed monthly with telephone interviews and in person at enrollment, three months and 12 months. OUTCOMES The dyspnea domain of the Chronic Respiratory Questionnaire (CRQ) at 12 months is the primary outcome variable. Secondary outcome variables include total and domain-specific CRQ scores; exercise tolerance and activity of daily living; health service use over the one-year study period; and direct and indirect costs of COPD treatment. ANALYSIS An intent-to-treat approach will be used as the primary analysis. The primary analysis will focus on the change in the CRQ dyspnea score using a two-sided t distribution based on 95% CIs. The same approach will be used for secondary continuous outcome variables. CONCLUSION The present trial will address two unresolved issues in pulmonary rehabilitation for patients with COPD: the short-term and long-term effectiveness of home-based pulmonary rehabilitation strategies. The authors will also determine if home-based pulmonary rehabilitation can reduce health service use (eg, hospitalizations and emergency visits) and if it can be done at a lower cost than the traditional hospital-based outpatient pulmonary rehabilitation.

Measurement Error in Prenatal Care Utilization: Evidence of Attenuation Bias in the Estimation of Impact on Birth Weight

Objective: Errors in the measurement of the timing and number of prenatal care visits may produce downward bias in estimates of the impact of prenatal care use on birth outcomes. This paper examines the extent of attenuation bias from measurement error in the estimation of the effect of prenatal care use on birth weight. Methods: Data were analyzed from the 1980 National Natality Survey, a nationally representative sample of live births with information on prenatal care utilization from three sources: birth certificates, medical provider surveys, and maternal surveys. The extent of attenuation bias in estimates of the impact of different measures of prenatal care use on birth weight was examined by comparing estimates robust to measurement error (including instrumental variables) with ordinary least squares results. Results: There is considerable disagreement in measures of prenatal care across the three data sources, with correlations in the utilization measures computed from different sources around 0.5. The results also show evidence of attenuation bias from measurement error in estimates of the impact of prenatal care on birth weight for both White and Black mothers. Attenuation bias was least severe for information from the birth certificate report of prenatal care. Conclusions: Because of measurement error, previous studies may have underestimated the effect of prenatal care utilization on birth weight. Corrected estimates, however, do not suggest that prenatal care is a major predictor of birth weight. In addition, part of what previous analyses have interpreted as adverse selection bias may in fact be attenuation bias due to measurement error.