Problem statement: Two of the techniques used in the meta-analysis of single-case research are calculating the percentage of nonoverlapping data (PND) and the percentage of data points that exceed the median of the baseline phase (PEM). The PND is a nonparametric approach in which the researcher calculates the percentage of data points in the treatment phase that exceed the highest point of the baseline phase’s distribution (or the lowest point if the targeted behavior is a problem behavior to be reduced). Even though PND can be calculated easily, it has a disadvantage if there is even one data point in the baseline phase over the top or below the bottom level, the PND score for that treatment phase is calculated as zero. Calculating the PEM was introduced in order to overcome this disadvantage. In this approach the effect size is calculated by finding the median of the baseline phase and drawing a horizontal line from this point through the intervention phase and then determining the percentage of data points over this line (or below this line for the problem behaviors).
Purpose of study: The purpose of this study was to investigate the effectiveness of the intervention studies that used single-subject design and targeted children and individuals with autism in Turkey.
Methods: Researchers reviewed studies conducted from 1990 to 2010 and calculated the PND and PEM scores for the selected studies. The researchers selected dissertations or studies that were published in peer reviewed journals that included intervention methods to teach skills/behaviors or reduce problem behaviors. Five articles, seven master’s theses, and four doctoral dissertations were included.
Findings and results: The mean effect sizes for the 14 studies were .85 for PND and .90 for PEM. The most effective intervention methods for teaching skills/behaviors and reducing problem behaviors are listed.
Conclusions and recommendations: The results of this study are discussed in terms of findings, the characteristics and limitations of the intervention methods and the characteristics of the study groups.
Keywords: Autism, effect size, intervention, single-subject design