The use of count data models in biomedical informatics evaluation research

Abstract

Objectives: Studies on the impact and value of health information technology (HIT) have often focused on outcome measures that are counts of such things as hospital admissions or the number of laboratory tests per patient. These measures with their highly skewed distributions (high frequency of 0s and 1s) are more appropriately analyzed with count data models than the much more frequently used variations of ordinary least squares (OLS). Use of a statistical procedure that does not properly fit the distribution of the data can result in significant findings being overlooked. The objective of this paper is to encourage greater use of count data models by demonstrating their utility with an example based on the authors' current work.

Target audience: Researchers conducting impact and outcome studies related to HIT.

Scope: We review and discuss count data models and illustrate their value in comparison to OLS using an example from a study of the impact of an electronic health record (EHR) on laboratory test orders. The best count data model reveals significant relationships that OLS does not detect. We conclude that comprehensive model checking is highly recommended to identify the most appropriate analytic model when the dependent variable being examined contains count data. This strategy can lead to more valid and precise findings in HIT evaluation studies.

Figure 1

Observed frequency distribution of the number of laboratory tests ordered during index emergency department (ED) visits for asthma patients.

Figure 2

A graphical comparison of the fit of ordinary least squares and count data models to the number of observed laboratory test orders.