title: Social deprivation and population density are not associated with small area risk of amyotrophic lateral sclerosis.
abstract: BACKGROUND
  Evidence of an association between areal ALS risk and population density has been previously reported. We aim to examine ALS spatial incidence in Ireland using small areas, to compare this analysis with our previous analysis of larger areas and to examine the associations between population density, social deprivation and ALS incidence.
  
  
  METHODS
  Residential area social deprivation has not been previously investigated as a risk factor for ALS. Using the Irish ALS register, we included all cases of ALS diagnosed in Ireland from 1995-2013. 2006 census data was used to calculate age and sex standardised expected cases per small area. Social deprivation was assessed using the pobalHP deprivation index. Bayesian smoothing was used to calculate small area relative risk for ALS, whilst cluster analysis was performed using SaTScan. The effects of population density and social deprivation were tested in two ways: (1) as covariates in the Bayesian spatial model; (2) via post-Bayesian regression.
  
  
  RESULTS
  1701 cases were included. Bayesian smoothed maps of relative risk at small area resolution matched closely to our previous analysis at a larger area resolution. Cluster analysis identified two areas of significant low risk. These areas did not correlate with population density or social deprivation indices.
  
  
  CONCLUSIONS
  Two areas showing low frequency of ALS have been identified in the Republic of Ireland. These areas do not correlate with population density or residential area social deprivation, indicating that other reasons, such as genetic admixture may account for the observed findings.
authors.affiliation: Academic Unit of Neurology, Trinity Biomedical Sciences Institute, Trinity College, Dublin 2, Ireland.
authors.forename: James P K
authors.initials: JP
authors.lastname: Rooney
authors.affiliation: Academic Unit of Neurology, Trinity Biomedical Sciences Institute, Trinity College, Dublin 2, Ireland.
authors.forename: Katy
authors.initials: K
authors.lastname: Tobin
authors.affiliation: School of Geography, Planning and Environmental Policy, University College Dublin Belfield, Dublin, Ireland.
authors.forename: Arlene
authors.initials: A
authors.lastname: Crampsie
authors.affiliation: Academic Unit of Neurology, Trinity Biomedical Sciences Institute, Trinity College, Dublin 2, Ireland.
authors.forename: Alice
authors.initials: A
authors.lastname: Vajda
authors.affiliation: Academic Unit of Neurology, Trinity Biomedical Sciences Institute, Trinity College, Dublin 2, Ireland.
authors.forename: Mark
authors.initials: M
authors.lastname: Heverin
authors.affiliation: Academic Unit of Neurology, Trinity Biomedical Sciences Institute, Trinity College, Dublin 2, Ireland.
authors.forename: Russell
authors.initials: R
authors.lastname: McLaughlin
authors.affiliation: School of Nursing and Human Sciences, Dublin City University, Dublin, Ireland.
authors.forename: Anthony
authors.initials: A
authors.lastname: Staines
authors.affiliation: Academic Unit of Neurology, Trinity Biomedical Sciences Institute, Trinity College, Dublin 2, Ireland; Department of Neurology, Beaumont Hospital, Beaumont, Ireland.
authors.forename: Orla
authors.initials: O
authors.lastname: Hardiman
mesh_terms: D000368:Aged; D000690:Amyotrophic Lateral Sclerosis / Q000453:epidemiology* / Q000209:etiology*; D001499:Bayes Theorem; D016000:Cluster Analysis; D005260:Female; D006801:Humans; D015994:Incidence; D007494:Ireland / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D011156:Population Density; D012307:Risk Factors; D012931:Social Environment; D000068916:Spatial Regression