Christopher M. Blanchette

Use of Stabilized Inverse Propensity Scores as Weights to Directly Estimate Relative Risk and Its Confidence Intervals

OBJECTIVES Inverse probability of treatment weighting (IPTW) has been used in observational studies to reduce selection bias. For estimates of the main effects to be obtained, a pseudo data set is created by weighting each subject by IPTW and analyzed with conventional regression models. Currently, variance estimation requires additional work depending on type of outcomes. Our goal is to demonstrate a statistical approach to directly obtain appropriate estimates of variance of the main effects in regression models. METHODS We carried out theoretical and simulation studies to show that the variance of the main effects estimated directly from regressions using IPTW is underestimated and that the type I error rate is higher because of the inflated sample size in the pseudo data. The robust variance estimator using IPTW often slightly overestimates the variance of the main effects. We propose to use the stabilized weights to directly estimate both the main effect and its variance from conventional regression models. RESULTS We applied the approach to a study examining the effectiveness of serum potassium monitoring in reducing hyperkalemia-associated adverse events among 27,355 diabetic patients newly prescribed with a renin-angiotensin-aldosterone system inhibitor. The incidence rate ratio (with monitoring vs. without monitoring) and confidence intervals were 0.46 (0.34, 0.61) using the stabilized weights compared with 0.46 (0.38, 0.55) using typical IPTW. CONCLUSIONS Our theoretical, simulation results and real data example demonstrate that the use of the stabilized weights in the pseudo data preserves the sample size of the original data, produces appropriate estimation of the variance of main effect, and maintains an appropriate type I error rate.

Healthcare use and costs in patients with chronic bronchitis initiating maintenance therapy with fluticasone/salmeterol vs other inhaled maintenance therapies

Objective: To compare risk of hospitalization or emergency department (ED) visit and healthcare costs in patients with chronic bronchitis initiating inhaled maintenance therapy with fluticasone propionate/salmeterol 250/50 mcg combination (FSC) versus other inhaled maintenance therapies. Design and methods: This retrospective cohort study assessed 9 217 patients from the PharMetrics administrative claims database enrolled from July 1997 to January 2005. Study subjects were persons with medical claims with diagnoses of chronic bronchitis (ICD-9-CM 491.xx) who also had pharmacy claims for FSC, salmeterol (SAL), inhaled corticosteroid (ICS), ipratropium (IPR), or ipratropium/albuterol combination (IAC). Persons with <12 months of continuous eligibility after the first prescription for initial maintenance therapy (“index date”) were excluded as were those receiving fluticasone propionate/salmeterol 100/50 mcg or 500/50 mcg (not indicated for patients with chronic bronchitis). For remaining persons, time to first hospitalization or ED visit during follow-up was compared for those receiving FSC versus other therapies using Cox proportional hazards regression. Healthcare costs during the first 12 months of follow-up were analyzed using generalized linear model regression.  Results: Receipt of FSC as initial inhaled maintenance therapy for chronic bronchitis (n = 1361) was associated with 41% lower risk of COPD-related hospitalization or ED visit compared with IPR (n < 1316) (p < 0.001). Adjusted costs of COPD-related hospitalization/ED visit were

Methylated Genes in Sputum Among Older Smokers With Asthma

507 (95% CI

One-year prevalence, comorbidities and cost of cachexia-related inpatient admissions in the USA

218–

Severity of COPD at initial spirometry-confirmed diagnosis: data from medical charts and administrative claims

1083) less with FSC than IPR. However, patients receiving FSC had

A Secondary Analysis of a Duration Response Association Between Selective Serotonin Reuptake Inhibitor Use and the Risk of Acute Myocardial Infarction in the Aging Population

261 (95% CI

Healthcare costs associated with initial maintenance therapy with fluticasone propionate 250 μg/salmeterol 50 μg combination versus anticholinergic bronchodilators in elderly US Medicare-eligible beneficiaries with COPD.

205–

Drug Use Patterns in Severely Mentally Ill Medicare Beneficiaries: Impact of Discontinuities in Drug Coverage

322) higher COPD-related pharmacy costs than those receiving IPR. Total COPD-related costs were

Comparative cost-effectiveness of a fluticasone- propionate/salmeterol combination versus anticholinergics as initial maintenance therapy for chronic obstructive pulmonary disease

90 lower with FSC than IPR although this difference was not significant (95% CI

The role of combination inhaled corticosteroid/long-acting β-agonist therapy in COPD management

330–