title: Explorations in statistics: the analysis of change.
abstract: Learning about statistics is a lot like learning about science: the learning is more meaningful if you can actively explore. This tenth installment of Explorations in Statistics explores the analysis of a potential change in some physiological response. As researchers, we often express absolute change as percent change so we can account for different initial values of the response. But this creates a problem: percent change is really just a ratio, and a ratio is infamous for its ability to mislead. This means we may fail to find a group difference that does exist, or we may find a group difference that does not exist. What kind of an approach to science is that? In contrast, analysis of covariance is versatile: it can accommodate an analysis of the relationship between absolute change and initial value when percent change is useless.
authors.affiliation: Division of Biostatistics and Bioinformatics, National Jewish Health, Denver, Colorado; Department of Biostatistics and Informatics, Colorado School of Public Health, University of Colorado Denver, Denver, Colorado; and EverettD@NJHealth.org.
authors.forename: Douglas
authors.initials: D
authors.lastname: Curran-Everett
authors.affiliation: Department of Mathematical Sciences, Clemson University, Clemson, South Carolina.
authors.forename: Calvin L
authors.initials: CL
authors.lastname: Williams
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D035843:Biomedical Research / Q000706:statistics & numerical data*; D003627:Data Interpretation, Statistical; D006801:Humans; D016018:Least-Squares Analysis; D015233:Models, Statistical; D010827:Physiology / Q000706:statistics & numerical data*; D012984:Software; D013997:Time Factors
keywords: absolute change; analysis of covariance; ordinary least-squares regression; percent change; symmetrized percent change