Christophe Genolini, René Écochard, Hélène Jacqmin-Gadda
Hospices Civils de Lyon, Service de Biostatistique, Lyon, France;Université Lyon 1, Villeurbanne, France;CNRS, UMR5558, Laboratoire de Biométrie et Biologie Evolutive, Villeurbanne, France.
UMR U1027, INSERM, Université Paul Sabatier, Toulouse, France;CeRSM (EA 2931), UFR STAPS, Université de Paris Ouest Nanterre La Défense, Nanterre, France.
Université de Bordeaux, ISPED, Centre INSERM U897-Epidemiology-Biostatistique, Bordeaux, France.
DOI: 10.4236/ojs.2013.34A004   PDF    HTML     6,050 Downloads   10,176 Views   Citations

Abstract

Longitudinal studies are those in which the same variable is repeatedly measured at different times. These studies are more likely than others to suffer from missing values. Since the presence of missing values may have an important impact on statistical analyses, it is important that they should be dealt with properly. In this paper, we present “Copy Mean”, a new method to impute intermittent missing values. We compared its efficiency in eleven imputation methods dedicated to the treatment of missing values in longitudinal data. All these methods were tested on three markedly different real datasets (stationary, increasing, and sinusoidal pattern) with complete data. For each of them, we generated nine types of incomplete datasets that include 10%, 30%, or 50% of missing data using either a Missing Completely at Random, a Missing at Random, or a Missing Not at Random missingness mechanism. Our results show that Copy Mean has a great effectiveness, exceeding or equaling the performance of other methods in almost all configurations. The effectiveness of linear interpolation is highly data-dependent. The Last Occurrence Carried Forward method is strongly discouraged.

Keywords

Imputation; Longitudinal Data; Intermittent Missing Values

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Conflicts of Interest

The authors declare no conflicts of interest.

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