The Comparative Fit Index (CFI) is a test of approximate model fit. CFI indexes the extent to which the proposed model fits better than a model that allows all phenotypes to be heritable, but assumes that they are genetically uncorrelated. The χ2 statistic can be used to calculate CFI by calculating a second χ2 statistic for a so-called independence model, i.e. a model that estimates genetic variances of all phenotypes but assumes all genetic covariances to be zero, such that ∑(θ) is diagonal. CFI is calculated using the formula below,50 with f = χ2 – degrees of freedom: f(Independence Model)−f(Proposed Model)f(Independence Model)
