Comparing definitions of purging disorder on point prevalence and associations with external validators.

Purging Disorder (PD) is characterized by recurrent purging after normal or small amounts of food among individuals with body image disturbance who are not underweight.1 PD is currently included as an example of an Eating Disorder Not Otherwise Specified (EDNOS) in the DSM-IV-TR,2 but recent research suggests that PD should be considered for inclusion as a separate provisional diagnostic category in need of further study in the DSM-V.3,4 Specifically, cross-sectional studies, laboratory research, and latent class analyses suggest that PD is distinct from normality1,5–11 and Bulimia Nervosa.1,5,8,11–15 In addition, epidemiological studies indicate that PD affects between 1.1% to 5.3% of women in their lifetimes.7,16 Thus, introducing PD in the DSM-V has the potential to move a substantial proportion of individuals from the heterogeneous17 and overpopulated18 EDNOS category to a potentially meaningful diagnosis. Including PD in the DSM-V would facilitate research by providing an official definition for the syndrome. Currently, several different definitions have been used,3,4 ranging from a broadly defined syndrome that includes purging and nonpurging compensatory behaviors19–22 to studies that restrict the term purging disorder to individuals who engage in self-induced vomiting or abuse of laxatives or diuretics.1,8,9,16,23 Further, the minimum frequency of purging behaviors has not been well-defined. While several studies have required purging at least twice per week,1,8,16,23 some have included individuals who purge at least once per week,14 and others have not specified a minimum frequency.19 The lack of consensus on how to define the central behavioral feature of PD in the literature invariably leads to inconsistent findings across studies. In addition, it is unclear which, if any, of the previously employed definitions would be best for inclusion in the DSM-V. The current study was designed to compare different potential definitions for PD to examine their impact on the point prevalence of PD as well as their ability to discriminate individuals with PD from non-eating disorder controls on external validators. Based on patterns observed across previous studies,7,9,16,19,23 we hypothesized that prevalence estimates would be greater for broader definitions than for more narrow definitions of the syndrome. In addition, given that 10–15% of eating disorders occur in men2,24 and that the most recent epidemiological study in the US supported a significantly higher prevalence of eating disorders in women compared to men,25 we hypothesized that prevalence estimates would be greater in women than in men. We did not have specific a priori definitions regarding which definitions would demonstrate stronger associations with external validators. If narrow definitions produce a more homogeneous group, then they might demonstrate stronger associations with external validators by reducing variability within the PD group. Conversely, if broad definitions do not reduce the homogeneity of the identified group, then association strength will not diminish as group size increases. Instead, associations may be more likely to be statistically significant due to increased sample size and power. Data come from an epidemiological study that utilized random sampling across three cohorts drawn from the same university in 1982, 1992, and 2002 (see Keel et al.26 for details). A prior study reported no significant change in PD point prevalence from 1990 to 2004;23 however, the present study spanned a longer time frame over which changes in Bulimia Nervosa point prevalence have been found.26 Thus, we conducted exploratory analyses to examine whether point prevalence estimates for PD differed across cohorts.