A methodological approach to identify external factors for indicator-based risk adjustment illustrated by a cataract surgery register

Table 4 Results of the univariate association analysis (under stratification for centres by means of the Mantel / Haenszel method) between putative external factors and two outcome indicators (refractive accuracy and visual rehabilitation) 2 – 5 weeks after cataract surgery, based on the combined data of three outpatient centres: Odds ratios (OR) and local 99% confidence intervals (CI)

	“Refractive accuracy” │SE – TR │ ≤ 0.5 dpt		“Visual rehabilitation” visual acuity cc ≥ 1.0
	OR	99% CI	OR	99% CI
Sociodemographic external factors
Age ≥ 80 versus age < 80	0.885	0.772–1.040	0.484	0.414–0.564
Female gender versus male gender	1.127	0.986–1.276	0.870	0.767–0.979
Quantitatively documented external factors
Baseline visual acuity cc ≤ 0.1 versus > 0.1	0.613	0.492–0.777	0.556	0.443–0.688
Severe nearsightedness (myopia; axial eye length ≥ 25 mm) versus normal eye length (22.01 – 24.9 mm)	0.613	0.486–0.744	0.993	0.805–1.209
Severe farsightedness (hyperopia, axial eye length ≤ 22 mm) versus normal eye length (22.01 – 24.9 mm)	0.737	0.587–0.919	0.541	0.434–0.672
Qualitatively documented external factors
Presence versus absence of at least one pre-existing condition (potentially) reducing visual acuity	0.915	0.804–1.047	0.508	0.442–0.571
Presence versus absence of at least one known previous ocular surgery	0.855	0.60–1.244	0.393	0.253–0.561
Presence versus absence of at least one surgically relevant ocular risk factor	0.773	0.675–0.888	0.732	0.632–0.840

TR: Target refraction, SE: Spherical equivalent 2–5 weeks after cataract surgery.
Visual acuity cc: best-corrected visual acuity 2–5 weeks after cataract surgery.