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BMC Med Res Methodol. 2007 Feb 15;7:9.

A cautionary note regarding count models of alcohol consumption in randomized controlled trials.

Author information

1
Department of Mathematics and Statistics, Smith College, Northampton, MA, USA. nhorton@email.smith.edu

Abstract

BACKGROUND:

Alcohol consumption is commonly used as a primary outcome in randomized alcohol treatment studies. The distribution of alcohol consumption is highly skewed, particularly in subjects with alcohol dependence.

METHODS:

In this paper, we will consider the use of count models for outcomes in a randomized clinical trial setting. These include the Poisson, over-dispersed Poisson, negative binomial, zero-inflated Poisson and zero-inflated negative binomial. We compare the Type-I error rate of these methods in a series of simulation studies of a randomized clinical trial, and apply the methods to the ASAP (Addressing the Spectrum of Alcohol Problems) trial.

RESULTS:

Standard Poisson models provide a poor fit for alcohol consumption data from our motivating example, and did not preserve Type-I error rates for the randomized group comparison when the true distribution was over-dispersed Poisson. For the ASAP trial, where the distribution of alcohol consumption featured extensive over-dispersion, there was little indication of significant randomization group differences, except when the standard Poisson model was fit.

CONCLUSION:

As with any analysis, it is important to choose appropriate statistical models. In simulation studies and in the motivating example, the standard Poisson was not robust when fit to over-dispersed count data, and did not maintain the appropriate Type-I error rate. To appropriately model alcohol consumption, more flexible count models should be routinely employed.

PMID:
17302984
PMCID:
PMC1810542
DOI:
10.1186/1471-2288-7-9
[Indexed for MEDLINE]
Free PMC Article

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