Analysis of relative change and initial value of biological studies

G. W. Williams, S. B. Forsythe, S. C. Textor, R. C. Tarazi

Research output: Contribution to journalArticlepeer-review

11 Scopus citations


In analyzing longitudinal data, the relationship between initial value (ξ1) and change in response to a maneuver or over time is often interest. This relationship is often determined by the Pearson correlation between χ1 and subsequent change (χ2 - χ1), but a correlation will often be obtained by mathematical necessity even when χ1 and χ2 are uncorrelated. It has been suggested that use of relative change, or (χ2 - χ1)/χ1, avoids these mathematical artifacts. By reference to early work by Pearson (Proc. R. Soc. London 60: 489-498, 1897) on an approximation to the correlation between ratios and by computer simulations, this paper shows that this solution is frequently not valid. An alternative approach to the analysis of the relationship between χ1 and relative change is presented and is illustrated by a study of renal blood flow.

Original languageEnglish (US)
Pages (from-to)R122-R126
JournalAmerican Journal of Physiology - Regulatory Integrative and Comparative Physiology
Issue number1
StatePublished - 1984

ASJC Scopus subject areas

  • Physiology
  • Physiology (medical)


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