Eyal Shahar1, Doron J Shahar. 1. Division of Epidemiology and Biostatistics, Mel and Enid Zuckerman College of Public Health, University of Arizona, Tucson, AZ, USA. shahar@email.arizona.edu
Abstract
BACKGROUND: The true change in the value of a variable between two time points is often assumed to be a cause or an effect of interest. To our knowledge, this assumption is based on intuition, rather than on any formal theoretical justification. METHODS: We used causal directed acyclic graphs to explore the causal properties of a change variable, and critically examined competing structures. RESULTS: Based on the proposed causal structure, a change variable (true change) is no more than a derived variable. It does not cause anything and is not of causal interest. CONCLUSIONS: A true change is not a variable in the physical world. Therefore, modelling the change between two time points is justified only in a few situations.
BACKGROUND: The true change in the value of a variable between two time points is often assumed to be a cause or an effect of interest. To our knowledge, this assumption is based on intuition, rather than on any formal theoretical justification. METHODS: We used causal directed acyclic graphs to explore the causal properties of a change variable, and critically examined competing structures. RESULTS: Based on the proposed causal structure, a change variable (true change) is no more than a derived variable. It does not cause anything and is not of causal interest. CONCLUSIONS: A true change is not a variable in the physical world. Therefore, modelling the change between two time points is justified only in a few situations.
Authors: Younghoon Kwon; Daniel A Duprez; David R Jacobs; Mako Nagayoshi; Robyn L McClelland; Eyal Shahar; Matthew Budoff; Susan Redline; Steven Shea; J Jeffrey Carr; Pamela L Lutsey Journal: J Am Heart Assoc Date: 2014-09-26 Impact factor: 5.501