In this issue of the Journal of Child Psychology and Psychiatry, Whittington et al. (2016) present a systematic review examining the efficacy of treatments for children with Tourette syndrome (TS). The systematic review reported the efficacy of three treatments for children with TS -(a) a2-adrenergic receptor agonists [clonidine and guanfacine (pill and tablet trials combined)], standardized mean difference (SMD) = (SMD = À0.54; 95% CI À0.92, À0.16; N = 601); (b) antipsychotic medications (SMD = À0.74; 95% CI À1.08, À0.40; N = 76); and (c) habit reversal training/comprehensive behavioral intervention (SMD = À0.64; 95% CI À0.99, À0.29; N = 133). This systematic review importantly extends on the results of previous meta-analyses in this area which combined pediatric and adult trial by demonstrating similar treatment effects when trials are restricted to pediatric populations (Weisman, Qureshi, Leckman, Scahill, & Bloch, 2013). Given that roughly one half to two thirds of children with TS have an improvement in tic symptoms that coincides with adolescents, it is hypothesized that adults with continued TS may represent a distinct subgroup of all individuals with TS and it remains unclear how generalizable neuroimaging, genetic, and treatment studies conducted in adults is to the larger population affected by tic symptoms as children.The current guidelines on treating children with TS are supported by the evidence presented in this and other systematic reviews (Murphy, Lewin, Storch, & Stock, 2013;Pringsheim et al., 2012;Roessner et al., 2011). Specific guidelines for the treatment of tic disorders in children suggest the use of antipsychotic medications and alpha-2 agonists for the treatment of tics (Murphy et al., 2013;Pringsheim et al., 2012;Roessner et al., 2011). North American guidelines also suggest the preferential use of alpha-2 agonists over antipsychotics as the first-line pharmacological treatment in children not because of differential efficacy but related to a favorable side-effect profile (Murphy et al., 2013;Pringsheim et al., 2012). These guidelines also suggest the use of behavioral treatments, when available for the treatment of tic disorders, but the availability of behavioral treatments for tic disorders is currently largely confined to select academic centers (Murphy et al., 2013;Pringsheim et al., 2012;Roessner et al., 2011).However, the evidence demonstrating efficacy of the alpha-2 agonists for the treatment of tics is much less substantial than suggested by the guidelines and results of previous systematic reviews. Specifically, although this systematic review (alpha-2 agonists: SMD = À0.54; 95% CI À0.92, À0.16; N = 601) and previous meta-analysis included adult and crossover trials (SMD = 0.31; 95% CI: 0.15-0.48), there was a large amount of heterogeneity between included trials [I 2 = 63% in Whittington et al. (2016) when the alpha-2 agonist pill and patch trials are combined] (Weisman et al., 2013). Statistical heterogeneity in meta-analysis measures the variation in study outcomes betwee...