title: The use and misuse of meta-analysis.
abstract: OBJECTIVE
  To demonstrate how the results of a meta-analysis can confuse rather than clarify therapeutic dilemmas if clinical heterogeneity among trials is ignored. Then to further discuss the qualities emergency physicians should expect from published meta-analyses if they are to affect clinical practice.
  
  
  METHODS
  The data and results were examined from 23 randomised controlled trials of selective decontamination of the digestive tract (SDD), which have been combined in a previous meta-analysis. These were reviewed to take account of clinical heterogeneity, particularly with regard to severity of patient illness.
  
  
  RESULTS
  Severity of patient illness predicts degree of reduction in mortality with SDD in a regression analysis: log odds ratio (OR) of death with SDD = -0.0074 - (0.0035 x control group mortality rate), P = 0.017. This is also true when trials are stratified into more and less severely ill patients: pooled OR (a) for CMR > 41% = 0.69 (0.54 to 0.89), with (b) CMR < 3% = 1.02 (0.86 to 1.21). This difference was not suggested by the original meta-analysis result.
  
  
  CONCLUSIONS
  Failure to take account of clinical heterogeneity between trials can mean a meta-analysis result ignores important differences in the effect of a treatment on different groups of patients. The discussion indicates how emergency physicians might guard against basing clinical practice on misleading meta-analysis results.
authors.affiliation: University of Manchester, United Kingdom.
authors.forename: F E
authors.initials: FE
authors.lastname: Lecky
authors.forename: R A
authors.initials: RA
authors.lastname: Little
authors.forename: P
authors.initials: P
authors.lastname: Brennan
mesh_terms: D000900:Anti-Bacterial Agents / Q000008:administration & dosage; D003422:Critical Care; D003625:Data Collection; D006801:Humans; D007422:Intestines / Q000382:microbiology; D015201:Meta-Analysis as Topic; D009026:Mortality; D016017:Odds Ratio; D016032:Randomized Controlled Trials as Topic; D012044:Regression Analysis; D012720:Severity of Illness Index
chemical_list: D000900:Anti-Bacterial Agents