title: Analyzing the occurrence of falls and its risk factors: some considerations.
abstract: OBJECTIVE
  Falls are a common problem facing elderly people and are associated with considerable mortality and morbidity. The objective of this paper is to study the application of the conditional model as an alternative for the statistical analysis of the occurrence of falls and their associated factors.
  
  
  METHODS
  Cohort study. We select all ninety-eight residents admitted during the year 2007 in a long-term care centre, Seville, Spain. Five models were fitted: Negative binomial, standard Cox for the first fall, standard Cox for all falls, Andersen-Gill model, and Prentice-Williams-Peterson model.
  
  
  RESULTS
  The crude incidence rate of falls was 26.3 per 100 person-months. The median time to fall decreases depending on the falls previously experienced, while the hazard rises. The AG's standard errors are between 1.4 and 2.7 times bigger than those estimated by Standard Cox. The major differences between marginal models were in the "Barthel 25-60" coefficient, where the conditional model attributed an HR=2.39 versus HR=3.77 estimated by the extension model.
  
  
  CONCLUSIONS
  As the risk increases depending on the falls previously suffered by an individual, the PWP-conditional model becomes an interesting alternative for obtaining unbiased and precise estimations of coefficients associated with possible risk factors of falls.
authors.affiliation: Unitat de Bioestadística, Facultat de Medicina, Universitat Autònoma de Barcelona, 08193 Cerdanyola del Vallès, Spain. albert.navarro@uab.cat
authors.forename: Albert
authors.initials: A
authors.lastname: Navarro
authors.forename: Iciar
authors.initials: I
authors.lastname: Ancizu
mesh_terms: D000058:Accidental Falls / Q000706:statistics & numerical data*; D000368:Aged; D000369:Aged, 80 and over; D015331:Cohort Studies; D005260:Female; D006707:Homes for the Aged / Q000706:statistics & numerical data*; D006801:Humans; D015994:Incidence; D016013:Likelihood Functions; D008297:Male; D009735:Nursing Homes / Q000706:statistics & numerical data*; D016016:Proportional Hazards Models; D012008:Recurrence; D018570:Risk Assessment / Q000379:methods; D012307:Risk Factors; D013030:Spain / Q000453:epidemiology; D016019:Survival Analysis