Augmented backward elimination: a pragmatic and purposeful way to develop statistical models

PLoS One. 2014 Nov 21;9(11):e113677. doi: 10.1371/journal.pone.0113677. eCollection 2014.

Abstract

Statistical models are simple mathematical rules derived from empirical data describing the association between an outcome and several explanatory variables. In a typical modeling situation statistical analysis often involves a large number of potential explanatory variables and frequently only partial subject-matter knowledge is available. Therefore, selecting the most suitable variables for a model in an objective and practical manner is usually a non-trivial task. We briefly revisit the purposeful variable selection procedure suggested by Hosmer and Lemeshow which combines significance and change-in-estimate criteria for variable selection and critically discuss the change-in-estimate criterion. We show that using a significance-based threshold for the change-in-estimate criterion reduces to a simple significance-based selection of variables, as if the change-in-estimate criterion is not considered at all. Various extensions to the purposeful variable selection procedure are suggested. We propose to use backward elimination augmented with a standardized change-in-estimate criterion on the quantity of interest usually reported and interpreted in a model for variable selection. Augmented backward elimination has been implemented in a SAS macro for linear, logistic and Cox proportional hazards regression. The algorithm and its implementation were evaluated by means of a simulation study. Augmented backward elimination tends to select larger models than backward elimination and approximates the unselected model up to negligible differences in point estimates of the regression coefficients. On average, regression coefficients obtained after applying augmented backward elimination were less biased relative to the coefficients of correctly specified models than after backward elimination. In summary, we propose augmented backward elimination as a reproducible variable selection algorithm that gives the analyst more flexibility in adopting model selection to a specific statistical modeling situation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Models, Statistical*

Grants and funding

DD, KL and GH were supported by the European Community's Seventh Framework Programme, grant number 241544, URLs http://ec.europa.eu/research/fp7/index_en.cfm and http://www.syskid.eu. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. All resources needed to complete this study (SAS software, computers, office programs, IT facilities) were provided by the Center for Medical Statistics, Informatics and Intelligent Systems, Medical University of Vienna (GH's and DD's department), using the Center's regular research budget.