Data were provided by GlaxoSmithKline (Greenford, England) and comprised 12 randomized controlled trials of various treatments for COPD undertaken over a period of approximately 10 years, involving a total of 8802 patients and amounting to over 6000 patient-years of information. Eight of these studies (7 published studies7- 13 and unpublished data from GlaxoSmithKline [“Randomised, 24-week, double-blind, placebo-controlled, parallel-group study followed by a 2-week, randomised, double-blind, run-out phase to evaluate the efficacy, safety, tolerability, and discontinuation of SB 207499 (15 mg twice daily) in patients with chronic obstructive pulmonary disease (COPD),” J. Christal et al, July 24, 2002]) followed patients for 6 months, 3 studies (2 published studies14- 15 and unpublished data from GlaxoSmithKline [“A double-blind, placebo-controlled parallel group study to evaluate the efficacy, safety, and tolerability of oral cilomilast (15 mg bd when given as maintenance treatment for 12 months to subjects with chronic obstructive pulmonary disease,” 2004]) followed patients for 1 year, and 1 followed patients for 3 years16; summary information for the individual trials is reproduced in Table 1. All trials recorded deaths, hospitalizations, and exacerbations of COPD (similarly defined as an acute respiratory episode requiring treatment with antibiotics and/or oral corticosteroids) but also included a wide variety of other measures at baseline offering potential prognostic factors. The data were pooled to predict exacerbations, hospitalizations, and death, employing prognostic factors that were available in each of the data sets. All of the studies included either the St George's Respiratory Questionnaire (SGRQ) or the Chronic Respiratory (Disease) Questionnaire (CRQ), but never both. These were assumed to be complements, and a single QOL variable was constructed from the standardized scores of the appropriate index (reversing the SGRQ scores so that a reduced standardized score represented a reduced QOL for both instruments). Where single observations were missing some of the prognostic factors, these were imputed using best subsets regression—the default imputation technique in Stata statistical software (version 8; StataCorp, College Station, Texas), the package used to undertake all analyses—to give a full rectangular data set.