The ideal definition of PD should not be too narrow where most people with an eating disorder are still diagnosed with an EDNOS. Nor should it be overly inclusive so that we are increasing diagnostic heterogeneity or overpathologizing normal variation. Point prevalence estimates indicate that including a broad range of compensatory eating behaviors in the definition of PD could reduce the number of individuals relegated to an EDNOS diagnosis. However, estimates suggest that this definition would label as “pathological” current behavioral patterns of approximately 1 in 20 college women. Further, analyses of external validators suggest that definitions that include a range of compensatory behaviors result in a more heterogeneous group that shows less robust distinctions from non-eating disorder controls on indicators of dysfunction compared to definitions that require purging behaviors.
While the external validators examined in this study distinguished between types of behaviors used in the definition of PD, they did not discriminate between minimum frequencies of behaviors. Within a narrow definition of purging, requiring behaviors at least once per week or twice per week was associated with nearly equivalent effect sizes in comparisons with the non-eating disorder group. These results are consistent with previous research finding no significant differences between EDNOS patients who purge twice per week and those who purge less frequently36
or between threshold and subthreshold frequencies of compensatory behaviors in the absence of binge eating.21
Given evidence that reducing minimum frequency of purging behaviors does not reduce syndrome homogeneity or clinical significance and the goal of forming a definition that is not overly narrow, results support setting the minimum frequency of purging behaviors to once per week.
Consistent with a previous study,23
there was no significant change in PD point prevalence from 1992 to 2002 for any definition. PD point prevalence decreased from 1982 to 1992 in women using the most narrow definition in which purging was required at least twice per week. However, interpretation of this finding is difficult as there was no significant difference between the 1982 and 2002 cohorts for this definition, indicating no reliable linear decrease over time. In addition, adjusting the minimum frequency to once per week resulted in a non-significant change in rates across cohorts. Thus, decreased prevalence from 1982 to 1992 may be a spurious finding. Of note, overall results indicated distinct epidemiological patterns for PD compared to those observed for Bulimia Nervosa in this sample,26
further supporting the validity of PD as a separate diagnostic entity.
The inclusion of a large sample of men and women, random sampling of college students, and comparison of definitions on external validators represent significant strengths of the present study. Indeed, the current study is the first to report prevalence rates of PD in men and gender differences for this syndrome. Gender differences are consistent with findings for Anorexia Nervosa and Bulimia Nervosa, suggesting that approximately 6% – 16% of individuals who suffer from PD are male. Thus, while PD is far more common in women than men, findings indicate that men should be examined in future research on PD. Interestingly, varying the minimum frequency criterion did not impact prevalence rates in men. This suggests that there may be a larger point of rarity between men who do and do not engage in recurrent purging behaviors to control weight or shape.
Despite these strengths, results should be interpreted in the context of several limitations. First, although sample size was large and random sampling was used, all participants were college students from a selective, northeastern university. Thus, caution should be used when generalizing findings to non-college or older individuals. Tempering this concern, our estimates of point prevalence were consistent with previous epidemiological studies. Previous studies reported point prevalence rates between 0.64%19
in women. We found very similar estimates using a narrow definition of purging in our large, random sample of college students (0.6% – 0.9%). Of note, PD point prevalence using a narrow definition of purging required at least twice per week (0.6% in women in the present study) is very similar to 0.8% reported in Crowther et al.,23
using the same criteria. Thus, converging prevalence estimates when utilizing similar diagnostic criteria across varying study groups support generalizability of study findings.
A second limitation is that all diagnoses were based on self-report surveys. Previous research37–39
and our own analyses support concurrent validity between survey-based and interview-based assessments of purging. However, it is possible that self-report assessments of fasting and compulsive exercise (nonpurging compensatory behaviors) that are not objectively defined for participants are more susceptible to misinterpretation and less psychometrically sound than interview-based assessments. Of note, we found good agreement between survey and interview-based assessments across a range of eating disorder definitions. In addition, reliance on available survey data led us to use Drive for Thinness as a proxy for overconcern with weight and to exclude individuals who purged following subjective binge episodes. Previous research indicates that many individuals with PD have subjective binge episodes.8,14,36
However, survey did not include adequate questions to reliably discriminate subjective from objective binge episodes. This led to a conservative approach in which we eliminated participants who reported any binge eating from a diagnosis of PD, and, thus, our prevalence estimates likely underestimate how common PD is. In addition, some of the criteria used in the current study may not be the best indicators for a formal definition of PD. Data collection for the current study began in 1982, before publication of eating disorder specific assessments, such as the Eating Disorder Examination (EDE),40
which would allow for comparison of definitions among multiple dimensions. Future studies utilizing assessments such as the EDE will be important for evaluating the impact of including subjective binge episodes on the homogeneity and clinical significance of PD. This work could also enhance our understanding of the nature of body image disturbance that best characterizes individuals with PD. In the current study, these criteria were held constant across definitions of PD and cannot account for our pattern of findings. Finally, a wider range of external validators are needed to further support a qualitative distinction between narrow and broad definitions of PD. Future research is needed to examine family history, health care utilization, and other indices of distress and impairment as external validators of varying definitions of PD.
The present study provides support for a meaningful distinction between PD defined by purging only (self-induced vomiting, laxative abuse, diuretic abuse) and a broader definition that encompasses any compensatory behavior (self-induced vomiting, laxative abuse, diuretic abuse, diet pill use, fasting, compulsive exercise). Results suggest that a broader definition would introduce heterogeneity among individuals with PD, reducing distinctions between PD and normality. In contrast, external validators did not distinguish between definitions with a minimum behavioral frequency of once versus twice per week. Given these results, purging in the form of self-induced vomiting, laxative abuse, or diuretic abuse at least once per week may represent the optimal starting point for defining the central behavioral feature of PD in future nosological schemes.