title: Using funnel plots in public health surveillance.
abstract: BACKGROUND
  Public health surveillance is often concerned with the analysis of health outcomes over small areas. Funnel plots have been proposed as a useful tool for assessing and visualizing surveillance data, but their full utility has not been appreciated (for example, in the incorporation and interpretation of risk factors).
  
  
  METHODS
  We investigate a way to simultaneously focus funnel plot analyses on direct policy implications while visually incorporating model fit and the effects of risk factors. Health survey data representing modifiable and nonmodifiable risk factors are used in an analysis of 2007 small area motor vehicle mortality rates in Alberta, Canada.
  
  
  RESULTS
  Small area variations in motor vehicle mortality in Alberta were well explained by the suite of modifiable and nonmodifiable risk factors. Funnel plots of raw rates and of risk adjusted rates lead to different conclusions; the analysis process highlights opportunities for intervention as risk factors are incorporated into the model. Maps based on funnel plot methods identify areas worthy of further investigation.
  
  
  CONCLUSIONS
  Funnel plots provide a useful tool to explore small area data and to routinely incorporate covariate relationships in surveillance analyses. The exploratory process has at each step a direct and useful policy-related result. Dealing thoughtfully with statistical overdispersion is a cornerstone to fully understanding funnel plots.
authors.affiliation: School of Public Health, University of Alberta, Edmonton, Canada. donald.schopflocher@ualberta.ca.
authors.forename: Douglas C
authors.initials: DC
authors.lastname: Dover
authors.forename: Donald P
authors.initials: DP
authors.lastname: Schopflocher
references.citation: Occup Environ Med. 2009 Nov;66(11):733-9
references.pmid: 19687020
references.citation: Qual Saf Health Care. 2003 Dec;12(6):458-64
references.pmid: 14645763
references.citation: Stat Med. 2000 Sep 15-30;19(17-18):2295-308
references.pmid: 10960854
references.citation: MMWR Suppl. 1988 May 6;37(5):1-18
references.pmid: 3131659
references.citation: J Clin Epidemiol. 2005 Sep;58(9):894-901
references.pmid: 16085192
references.citation: Qual Saf Health Care. 2005 Oct;14(5):347-51
references.pmid: 16195568
references.citation: BMJ. 2001 Jul 14;323(7304):101-5
references.pmid: 11451790
references.citation: Stat Med. 2005 Apr 30;24(8):1185-202
references.pmid: 15568194
references.citation: BMJ. 1998 Jun 6;316(7146):1701-4; discussion 1705
references.pmid: 9614016
references.citation: Int J Qual Health Care. 2004 Aug;16(4):309-15
references.pmid: 15252005