Sex differences in prevalence have been reported in several mental disorders. For example, the prevalence of trichotillomania, anorexia nervosa, and bulimia nervosa are reported to be as much as 10 times more common in girls than boys (American Psychiatric Association, 2013). By contrast, autism spectrum disorder (ASD) is reportedly four to five times more common in boys compared to girls (Baird et al., 2006; Centers for Disease Control and Prevention [CDC], 2016). The accuracy of this ratio has been questioned with some authors citing the potential gender bias in diagnostic instruments as many of the measures were developed and standardized in predominantly male samples (Kreiser & White, 2014). In addition, behavioral characteristics such as stereotypic and disruptive behavior may be more pronounced in boys, which may increase the likelihood that boys will come to clinical attention (Mandy, Chilvers, Chowdhury, Salter, Seigal, & Skuse, 2011). On the other hand, others contend that male gender increases the risk for ASD (Baron-Cohen, Lombardo, Auyeung, Ashwin, Chakrabarti, & Knickmeyer, 2011).
In the 2007 report by the CDC, the prevalence of ASD was 1 in 150 children (CDC, 2007). The current prevalence estimate is 1 in 68 children (CDC, 2016). Despite the rise in the estimated prevalence, the male-to-female ratio has remained remarkably consistent (see CDC, 2007, 2016). Current prevalence estimates are 1 in 42 for boys and 1 in 189 for girls – nearly 5:1 (CDC, 2016).
If these prevalence estimates of ASD in boys and girls are accurate, then the male:female ratio in several large-scale clinical trials is indeed representative. For example, we tallied the male:female ratio in five federally-funded multisite trials in children with ASD (Aman et al., 2009; Bearss et al., 2015; King et al., 2009; Research Units on Pediatric Psychopharmacology Autism Network 2002; Research Units on Pediatric Psychopharmacology Autism Network, 2005; Scahill et al., 2015). Across these trials, there were 682 participants (age 4 to 17 years); 585 were boys and 97 were girls. Given the relatively small number of girls in each study, it was not possible to evaluate sex as a moderating variable in any of these studies. A similar conclusion was reported in a review of 5 meta-analyses on the effectiveness of Early Intensive Behavioral Interventions for children with ASD (Reichow, 2011). In the absence of larger samples of girls with ASD in treatment studies, it is unclear how girls respond to the currently available evidence-based interventions.
Given the current state of knowledge, we can either assume that there is no difference in treatment response in girls or begin a line of research to test this assumption. If we assume no difference based on sex, we simply accept that the results of empirically supported treatments apply to boys and girls. However, if there is reason to believe that girls may respond differentially to specific interventions, it may be informative to enroll female-exclusive samples into treatment programs with demonstrated efficacy in boys. With support from the Autism Science Foundation, we are about to launch an evidenced-based social engagement intervention in girls with ASD (Shillingsburg, Bowen, & Shapiro, 2014). We hope that other treatment programs will pursue this line of research in order to promote our understanding of girls with ASD.
Tom Cariveau, PhD, BCBA-D, is Postdoctoral Psychology Fellow, M. Alice Shillingsburg, PhD, BCBA-D, is Assistant Professor of Pediatrics, Caitlin Delfs, PhD, BCBA-D, is Assistant Professor of Pediatrics, and Lawrence Scahill, MSN, PhD, is Professor of Pediatrics at the Marcus Autism Center and Emory School of Medicine. Please address correspondence to Dr. Tom Cariveau, 1920 Briarcliff Rd NE, Atlanta, GA 30324, email email@example.com, or call (404) 785-9363.
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