title: Hierarchical log linear analysis of admission blood parameters and clinical outcome following traumatic brain injury.
abstract: OBJECTIVE
  Numerous statistical methods have been utilised to generate predictive models that identify clinical and biochemical parameters of prognostic value following traumatic brain injury. While these methods provide an accurate statistical description between these variables and outcome, they are difficult to interpret intuitively. Hierarchical log linear analysis can be utilised to present the complex interactions between these variables and outcome visually.
  
  
  METHODS
  We compiled a database of 327 traumatic brain injury patients, their admission blood parameters, clinical admission parameters, and 6-month Glasgow Outcome Score. Seven variables (age, injury severity, Glasgow Coma Score, glucose, albumin, haemoglobin, white cell count) that correlated with outcome in a univariate analysis and two further variables, included on the basis of biological plausibility, (abnormal clotting and magnesium) were used to derive and present a hierarchical log linear model.
  
  
  RESULTS
  Seventeen (out of an original forty-five possible) inter-relationships between the chosen variables were identified as remaining in the hierarchical log linear model. This data is presented pictorially in a hierarchy demonstrating the directness of the statistical association between each of the variables and dichotomised outcome. Four variables within the hierarchical log linear model (age, raised serum glucose, low haemoglobin, Glasgow Coma Score) had a direct independent statistical relationship with outcome. The remaining five variables only had a statistical relationship with outcome via at least one other variable.
  
  
  CONCLUSIONS
  Hierarchical log linear analysis allows the presentation of multivariate, categorical data sets in a pictorial and more easily interpretable fashion.
authors.affiliation: Division of Neurosurgery, University of Cambridge, Cambridge, UK. adelhelmy@cantab.net
authors.forename: Adel
authors.initials: A
authors.lastname: Helmy
authors.forename: Ivan
authors.initials: I
authors.lastname: Timofeev
authors.forename: Christopher R
authors.initials: CR
authors.lastname: Palmer
authors.forename: Alison
authors.initials: A
authors.lastname: Gore
authors.forename: David K
authors.initials: DK
authors.lastname: Menon
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Hutchinson
mesh_terms: D018806:APACHE; D001774:Blood Chemical Analysis / Q000706:statistics & numerical data*; D001930:Brain Injuries / Q000175:diagnosis*; D015600:Glasgow Coma Scale / Q000706:statistics & numerical data; D023261:Glasgow Outcome Scale / Q000706:statistics & numerical data; D006801:Humans; D015601:Injury Severity Score; D007902:Length of Stay / Q000706:statistics & numerical data; D016014:Linear Models; D008485:Medical Audit; D008875:Middle Aged; D015999:Multivariate Analysis; D011183:Postoperative Complications / Q000097:blood*; D011237:Predictive Value of Tests; D012189:Retrospective Studies; D013223:Statistics as Topic; D006113:United Kingdom