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Why covariance analysis should replace increment analysis of variance in caries studies
Author(s) -
Slakter Malcolm J.,
Wu Bill Y.
Publication year - 1981
Publication title -
community dentistry and oral epidemiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.061
H-Index - 101
eISSN - 1600-0528
pISSN - 0301-5661
DOI - 10.1111/j.1600-0528.1981.tb00349.x
Subject(s) - analysis of variance , analysis of covariance , mixed design analysis of variance , repeated measures design , statistics , one way analysis of variance , covariate , medicine , statistical analysis , covariance , mathematics
Consider a caries study where experimental units are a) randomly assigned lo groups, b) premeasured on DMFS, c) administered a specified treatment depending on group membership, and d) postmeasured on DMFS. Traditional analysis of these data consists of analysis of variance of the increment scores (increment ANOVA). In place of increment ANOVA, others have suggested analysis of covariance with the postmeasure as criterion and the premeasure as covariate (ANOCOV). The present paper examines and documents the following: 1) Increment ANOVA and ANOCOV test the same null hypothesis. 2) Increment ANOVA and ANOCOV have exactly the same assumptions. 3) Increment ANOVA is usually less precise than ANOCOV. 4) The same concern for violations of assumptions must be expressed with increment ANOVA as with ANOCOV (see No. 2 above). 5) ANOCOV should replace increment ANOVA in caries studies (see points 1‐4).