Eating Disorders and Obsessive-Compulsive Disorder: An ...

and compared 70 AN patients who had been assessed or treated 10 years earlier with
a cohort of 98 non-clinical controls. Results indicated that 54.3% of the AN group met
lifetime prevalence for BN when compared with only 2% of the comparison group. In
addition, the majority of crossover occurred within two years of the initial AN diagnosis,
which lead the authors to conclude that AN presented a significant risk for the
development of BN (Sullivan et al., 1998).
The largest assessment of diagnostic crossover among eating disorder
populations was conducted by Tozzi and colleagues (2005). These authors examined
350 AN and 88 BN patients, and assessed crossover from AN-Restricting to BN and
vise versa. It was found that 36% of patients with AN-Restricting developed BN, whilst
27% of BN patients went on to develop AN-Restricting. This latter finding was
surprising on the basis that previous research had estimated crossover from BN to AN
as being as low as 0% to 4% (Collings & King, 1994; Fairburn et al., 1995; Fairburn,
Cooper, Doll, Norman, & O’Connor, 2000; Fichter & Quadflieg, 1997; Johnson-Sabine,
Reiss, & Dayson, 1992; Swift, Ritholz, Kalin, & Kaslow, 1987; Tozzi et al., 2005).
Consistent with earlier studies (Eckert et al., 1995; Eddy et al., 2002; Strober et al.,
1997), 91% of the crossover between AN-Restricting and BN, and 77% of the
crossover between BN and AN-Restricting, occurred within five years of developing the
principal eating disorder.
Such a high overlap between eating disorder categories has prompted
researchers to identify whether the conceptualisation of these disorders may be better
suited to dimensional models that focus on preoccupation with eating, shape, and
weight; obsessionality; and engaging in binge eating (Williamson et al., 2002, 2005).
Classification models have emerged based on symptom counts and the presence or
absence of certain disordered eating behaviours (Birmingham, Touyz, & Harbottle,
2009; Bulik, Sullivan, & Kendler, 2000; Wade et al., 2006a). Wade and colleagues
(2006a) adopted a novel approach by examining the incidence of lifetime eating
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