title: The interactions between municipal socioeconomic status and age on hip fracture risk.
abstract: CONCLUSIONS
  Age modifies the effect of area-level socioeconomic status (SES) in the risk of fragility hip fractures (HF). For older individuals, the risk of HF increases as SES increases. For younger individuals, risk of HF increases as SES decreases. Our study may help decision-makers to better direct the implementation of political decisions.
  
  
  BACKGROUND
  The effect of socioeconomic status (SES) on hip fracture (HF) incidence remains unclear. The objective of this study is to evaluate the association between HF incidence and municipality-level SES as well as interactions between age and SES.
  
  
  METHODS
  From the Portuguese Hospital Discharge Database, we selected hospitalizations (2000-2010) of patients aged 50+, with HF diagnosis (codes 820.x, ICD9-CM), caused by traumas of low/moderate energy, excluding bone cancer cases and readmissions for aftercare. Municipalities were classified according to SES (deprived to affluent) using 2001 Census data. A spatial Bayesian hierarchical regression model (controlling for data heterogeneity and spatial autocorrelation), using the Poisson distribution, was used to quantify the relative risk (RR) of HF, 95% credible interval (95%CrI), and analyze the interaction between age and SES after adjusting for rural conditions.
  
  
  RESULTS
  There were 96,905 HF, 77.3% of which were on women who, on average, were older than men (mean age 81.2±8.5 vs 78.2±10.1 years) at admission (p<0.001). In women, there was a lower risk associated with better SES: RR=0.83 (95%CrI 0.65-1.00) for affluent versus deprived. There was an inverse association between SES and HF incidence rate in the youngest and a direct association in the oldest, for both sexes, but significant only between deprived and affluent in older ages (≥75 years).
  
  
  CONCLUSIONS
  Interaction between SES and age may be due to inequalities in lifestyles, access to health systems, and preventive actions. These results may help decision-makers to better understand the epidemiology of hip fractures and to better direct the available funding.
authors.affiliation: INEB, Instituto de Engenharia Biomédica, Rua do Campo Alegre, 823, 4150-180, Porto, Portugal, coliveir@ineb.up.pt.
authors.forename: C M
authors.initials: CM
authors.lastname: Oliveira
authors.forename: T
authors.initials: T
authors.lastname: Economou
authors.forename: T
authors.initials: T
authors.lastname: Bailey
authors.forename: D
authors.initials: D
authors.lastname: Mendonça
authors.forename: M F
authors.initials: MF
authors.lastname: Pina
mesh_terms: D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006620:Hip Fractures / Q000453:epidemiology*; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D011174:Portugal / Q000453:epidemiology; D012111:Residence Characteristics; D012307:Risk Factors; D012923:Social Class