Abstract
Observational studies in glaucoma patients can provide important evidence on treatment effects, especially for combination therapies which are often used in reality. But the success relies on the reduction of selection bias through methods such as propensity score (PS) weighting. The objective of this study was to assess the effects of five glaucoma treatments (medication, laser, non-laser surgery (NLS), laser + medication, and NLS + medication) on 1-year intraocular pressure (IOP) change. Data were collected from 90 glaucoma subjects who underwent a single laser, or NLS intervention, and/or took the same medication for at least 6 months, and had IOP measures before the treatment and 12-months after. Baseline IOP was significantly different across groups (p = 0.007) and this unbalance was successfully corrected by the PS weighting (p = 0.81). All groups showed statistically significant PS-weighted IOP reductions, with the largest reduction in NLS group (−6.78 mmHg). Baseline IOP significantly interacted with treatments (p = 0.03), and at high baseline IOP medication was less effective than other treatments. Our findings showed that the 1-year IOP reduction differed across treatment groups and was dependent on baseline IOP. The use of PS-weighted methods reduced treatment selection bias at baseline and allowed valid assessment of the treatment effect in an observational study.
Highlights
Unlike randomized controlled trials, observational studies often have pre-treatment characteristics that are associated with treatment assignment, thereby introducing confounding effects when evaluating treatment efficacy
We estimated the average 1-year intraocular pressure (IOP) changes for all treatment groups with 95% confidence intervals (CIs) either unadjusted or adjusted by the propensity score (PS) weights from generalized boosted model (GBM) (Table 2)
Our goal was to assess the effect of medication, laser, NLS, and their combination on 1-year IOP reduction in a retrospective analysis of a longitudinal cohort of glaucoma subjects
Summary
Observational studies often have pre-treatment (baseline) characteristics that are associated with treatment assignment, thereby introducing confounding effects when evaluating treatment efficacy. The propensity score (PS) method is commonly used in observational studies to reduce bias caused by different patient characteristics at baseline aiming to mimic treatment randomization[8]. PS is defined as the probability of receiving treatment assignment conditional on observed baseline covariates[9], and combining all baseline variables into a single score is convenient when there are a large number of baseline covariates[10]. The PS weighting method is useful because all participants can be included in the study, unlike PS matching. We applied the PS weighting method for a longitudinal cohort of subjects with glaucoma that were treated with a single treatment or a combination of treatments, including medication, laser, and NLS
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