“…According to the Wald test included in the HLM approach, this reduction in challenging behavior was statistically significant. These PND and HLM findings correspond to the findings of other meta-analyses published in the domain of persons with disabilities: Behavioral interventions are on average effective in reducing challenging behavior in individuals with disabilities (Didden, Korzilius, van Oorsouw, & Sturmey, 2006;Harvey, Boer, Meyer, & Evans, 2009;Heyvaert, Maes, & Onghena, 2010;Heyvaert, Maes, Van den Noortgate, Kuppens, & Onghena, 2012;Heyvaert, Saenen, Maes, & Onghena, 2014b;Vanderkerken et al, 2013). Nonetheless, based on the likelihood ratio test included in the HLM approach, we found that the intervention effects varied significantly over the participants and studies included in the dataset.…”