Effectiveness of inhaled corticosteroids in chronic obstructive pulmonary disease: immortal time bias in observational studies.

摘要: Recent large-scale cohort studies that reported an important reduction in mortality and chronic obstructive pulmonary disease (COPD) morbidity with inhaled corticosteroids may be biased. We used a population-based of Saskatchewan residents 55 years age or over, first hospitalized for COPD during 1990 to 1997, study this potential bias. These 979 subjects were followed year from discharge until their readmission death (389 subjects). Inhaled corticosteroid exposure was measured as any dispensing within 90 days after discharge. Cox's proportional hazards model compare the time-fixed analysis employed recent alternative time-dependent analysis. The adjusted rate ratio 0.69 (95% CI: 0.55-0.86) use days, whereas 1.00 0.79-1.26). With analysis, ratios affected by length period, decreasing 0.98 15-day period 0.51 365 but remained stable between 1.06 0.94 hospitalization not found reduce morbidity. Although observational can valuable, reports reductions are biased inappropriate allocation immortal time.