{
  "package" : "hl7.terminology@6.3.0",
  "definition" : "The percentage of total variation across studies that is due to heterogeneity rather than chance. I2 can be readily calculated from basic results obtained from a typical meta-analysis as i2 = 100%×(q - df)/q, where q is cochran's heterogeneity statistic and df the degrees of freedom. Negative values of i2 are put equal to zero so that i2 lies between 0% and 100%. A value of 0% indicates no observed heterogeneity, and larger values show increasing heterogeneity. Unlike cochran's q, it does not inherently depend upon the number of studies considered. A confidence interval for i² is constructed using either i) the iterative non-central chi-squared distribution method of hedges and piggott (2001); or ii) the test-based method of higgins and thompson (2002). The non-central chi-square method is currently the method of choice (higgins, personal communication, 2006) – it is computed if the 'exact' option is selected.",
  "system" : "http://terminology.hl7.org/CodeSystem/attribute-estimate-type",
  "property" : [ ],
  "codesystem" : "1aaf1644-33ab-5e19-a613-1268cb038189",
  "concept_id" : "1ed8b951-b693-5ba5-a845-f5d15e2c24d7",
  "ancestors" : {
    "0000420" : 0
  },
  "id" : "11bbe6ba-b680-4282-9184-f43e47ff89d8",
  "code" : "0000420",
  "display" : "I-squared",
  "version" : "1.0.1"
}