title: The effect of free health care on polypharmacy: a comparison of propensity score methods and multivariable regression to account for confounding.
abstract: OBJECTIVE
  Differing healthcare access has implications for public health. In Ireland, eligibility for free public health care is means tested. Here, we examine the association between healthcare access and polypharmacy while accounting for underlying socio-economic and health status differences.
  
  
  METHODS
  Self-reported regular medication use, history of diagnosed health conditions, disability, socio-demographics, and objective measures of depression and anxiety for adults aged 50-69 years (n = 5796) were ascertained from the population-representative Irish Longitudinal Study on Ageing. Objective measures of frailty, cognition, hypertension, and body mass index were also assessed for 4241 participants. The associations between free healthcare access and polypharmacy and use of 15 medication classes were estimated using multivariable modified Poisson regression, adjustment for the propensity score, and inverse probability of treatment weighting by the propensity score.
  
  
  RESULTS
  Polypharmacy was reported by 22% and 7% of the 1932 and 3864 participants with and without public healthcare coverage. Public patients had a 21-38% greater risk of polypharmacy depending on the method used to account for confounding. Results were less robust using propensity score weighting. There was evidence that classes of cardiovascular drugs, drugs for acid-related disorders, and analgesics were used more commonly in public patients. Associations were mostly unaffected after also accounting for objective health measures but were significantly attenuated after accounting for frequency of healthcare visits.
  
  
  CONCLUSIONS
  Publically funded health care in Ireland leads to greater medication use in people aged 50-69 years. This may reflect over-prescribing to public patients or restricted use among those who pay out of pocket.
authors.affiliation: The Irish Longitudinal Study on Ageing (TILDA), Trinity College Dublin, Dublin, Ireland; Department of Medical Gerontology, Trinity College Dublin, Dublin, Ireland.
authors.forename: Kathryn
authors.initials: K
authors.lastname: Richardson
authors.forename: Rose Anne
authors.initials: RA
authors.lastname: Kenny
authors.forename: Kathleen
authors.initials: K
authors.lastname: Bennett
mesh_terms: D000368:Aged; D015986:Confounding Factors, Epidemiologic; D003695:Delivery of Health Care / Q000191:economics* / Q000639:trends; D005260:Female; D006801:Humans; D057970:Inappropriate Prescribing / Q000191:economics* / Q000639:trends; D007494:Ireland / Q000453:epidemiology; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D009313:National Health Programs / Q000191:economics* / Q000639:trends; D019338:Polypharmacy; D057216:Propensity Score
keywords: confounding; health service use; pharmacoepidemiology; polypharmacy; propensity score adjustment