Equine-assisted Therapy for Therapy-resistant Adolescents With Autism Spectrum Disorders, a Replicated AB-design

Change from baseline on the Emotion dysregulation Index (EDI) after start of the intervention

The EDI-short form is a validated, change-sensitive, 13-item caregiver report measure of emotion regulation impairment for individuals who are at least 6 years of age. The scale used is Not at all=0, Mild=1, Moderate=2, Severe=3, or Very Severe=4. The EDI short form includes two scales: a 7-item Reactivity Index and a 6-item Dysphoria Index. Index raw scores will be converted into t-scores.

Change from baseline of Quality of life as scored on the KIDSCREEN after 15 weeks and 1 year

The KIDSCREEN-27 is a generic health-related quality of life (HRQOL) questionnaire for children aged 8-18 years. There is a self-complete version (child and a proxy version (parent). It consists of 27 items measuring five dimensions: physical well-being, psychological well-being, parent relations \& autonomy, social support \& peers and school environment. Items are answered on a five-point Likert-type scale assessing frequency (never (1), seldom (2), sometimes (3), often (4), and always (5)) or intensity (not at all (1), slightly (2), moderately (3), very (4), and extremely (5)) with a one-week recall period. Negatively formulated items are recoded and the sum scores for respective dimensions are converted into T scores with a mean of 50 and a standard deviation (SD) of 10. Higher scores indicate better HRQOL.

Change from baseline of severity of autism spectrum symptoms as measured on the Social Responsiveness Scale (SRS-2) after 15 weeks and 1 year

The Social Responsiveness Scale (SRS-2) measures deficits in social behavior associated with ASD and can be used to assess the severity of symptoms in ASD. The questionnaire will be completed by multiple raters (parents and teachers). The SRS-2 consists of 65 items scored in a Likert-like scale format ranging from not true=1, sometimes true=2, often true=3 to almost always true =4. It is designed to identify social impairment intrinsic to ASD and to quantify its severity across the duration of the treatment. A total score and five treatment subscale scores (Social Awareness; Social Cognition; Social Communication; Social Motivation; and Restricted Interests and Repetitive Behavior) are obtained. The accepted diagnostic criteria (cut point) for the SRS-2 for the association with a diagnosis of ASD are:\<=59 (normal); 60-75 (mild to moderate ASD); and =\>76 (severe ASD).

Change from baseline on the Goal Attainment Scale (GAS) after the intervention after 15 weeks

Goal Attainment Scale is a method of scoring the extent to which the patient's individual goals are achieved in the course of the intervention. In effect, each patient has his own outcome measure, but this is scored in a standardized way as to allow statistical analysis. Each goal is rated on a six-point scale, capturing the degree of attainment for each goal area: The present situation is scored -2 (stable). When the patient improves, but achieves less than the expected level this is scored -1 and the expected level is scored 0. When he achieves a better than expected outcome this is scored +1 (somewhat better than the goal) or +2 (much better). Achieving a worse than expected outcome is scored -3 (somewhat worse) In this study, a maximum of 3-4 goals are identified, which are incorporated into a single GAS score.

Change from baseline of self-esteem as measured on the The Rosenberg Self-Esteem Scale (RSES) after 15 weeks and 1 year

The Rosenberg Self-Esteem Scale (RSES) \[31\] will be used to assess self-esteem. It is a widely used 10-item Likert-scale self-esteem measure. Items are answered on a four-point scale - ranging from strongly agree to strongly disagree - measuring positive and negative feelings towards the self. The Dutch version of the RSES is found to be a one-dimensional scale with high internal consistency and congruent validity and a Cronbach's alpha of 0.89