Assessing the validity of health administrative data compared to population health survey data for the measurement of low back pain

Low back pain (LBP) is a high burden condition that lacks routine surveillance data. Health administrative data may be used for surveillance, but its validity for measuring LBP in the general population has not been established. We aimed to 1) determine the validity of health administrative data to measure LBP compared to self-reported LBP in a population-based sample of Ontario adults; 2) describe the differences in characteristics of LBP cases based on data sources. Adult respondents (≥18 years) of the Canadian Community Health Survey (CCHS) from 2003-2012 were included (N=150,695). CCHS data were individually-linked to health administrative data, including Ontario Health Insurance Plan and hospitalization data. The reference standard was defined as self-reported back problem diagnosed by a health professional in the CCHS. LBP measurement from billing records was defined as ≥1 physician billing/procedural code for LBP during the year preceding CCHS interview date. We measured concurrent validity by comparing prevalence, agreement (Kappa), and accuracy (sensitivity, specificity, positive and negative predictive values (PV)) of administrative data to measure LBP. LBP prevalence was higher (21.2%) using self-reported than administrative data (10.2%), and agreement was low (kappa=0.21). Administrative data had sensitivity 23.9% (95% CI 23.1-24.6), specificity 93.4% (95% CI 93.2-93.7), positive PV 50.4% (95% CI 49.1-51.7), and negative PV 82.0% (95% CI 81.7-82.3). Characteristics of LBP cases based on datasets differed in sex, health/behaviour characteristics, and allied healthcare utilization. Using health administrative data significantly underestimates prevalence of LBP. This can lead to misclassification bias that is likely non-differential in epidemiological studies.