Peer groups are aggregations of health regions that share similar socio-economic and demographic characteristics, based on 2006 Census data. These are useful in the analysis of health regions, where important differences may be detected by comparing health regions within a peer group. The ten peer groups are identified by the letters A through J, which are appended to the health region 4-digit code. Caution should be taken when comparing data for the peer groups over time due to changes in the peer groups. For more information on the peer groups classification, consult Statistics Canada's publication "Health Indicators" (catalogue number 82-221-XWE). See also: http://www.statcan.gc.ca/pub/82-221-x/2011002/regions/hrt4-eng.htm.