Explorations in statistics: the analysis of change

Adv Physiol Educ. 2015 Jun;39(2):49-54. doi: 10.1152/advan.00018.2015.


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.

Keywords: absolute change; analysis of covariance; ordinary least-squares regression; percent change; symmetrized percent change.

Publication types

  • Review

MeSH terms

  • Analysis of Variance
  • Animals
  • Biomedical Research / statistics & numerical data*
  • Data Interpretation, Statistical*
  • Humans
  • Least-Squares Analysis
  • Models, Statistical*
  • Physiology / statistics & numerical data*
  • Software
  • Time Factors