This study aims to investigate the efficacy of guided self-help Acceptance Commitment Therapy (ACT) for adults who have a diagnosis for Autistic Spectrum Disorder (ASD) and are experiencing psychological distress (stress, anxiety or depression).

This is a repeated measures design, using a single case experimental design (SCED) over a period of fourteen weeks. Each participant (n=8) with be asked to complete weekly measures and shortened measures every three days, while they read an ACT guided self-help bibliotherapy. For more information about the measures, please see outcome measure section. The ACT guided bibliotherapy will be administered to each participant on a weekly basis, over eight weeks.

Participants will be asked to complete outcome measures at two week and at four weeks post intervention.

INTRODUCTION High levels of psychiatric co-morbidity have been found with adults who receive a diagnosis of Autistic Spectrum Disorder (ASD); including stress, anxiety, depression and OCD.

Acceptance and Commitment Therapy (ACT) is a psychotherapeutic approach and is referred to as a "third wave" CBT. There have been over one hundred randomized control trials (RCTs) supporting the efficacy of ACT for different types of distress and severity. Researchers conducted an ACT based group, for students with ASD; the results indicated that levels of stress, hyperactivity and emotional distress were reduced in the treatment group, compared to classes as unusual. Results were maintained or improved at a two month follow up. However, little is still known about the efficacy of ACT for adults with ASD who experience.

This research will indicate if guided ACT self-help facilitates increases psychological flexibility for adults with ASD, which is known to be less developed in people with ASD. Psychological flexibility mediates the experience of psychological distress, for example depression, anxiety and stress, which are known to be highly prevalent in this population. Currently, there are mixed results in relation to effectiveness of CBT; very few researchers have measured the effectiveness of ACT to increase psychological flexibility in an adult ASD population and determine if this mediates a reduction in psychological distress.

PURPOSE OF THE STUDY This research will add to the knowledge about how ACT guided self-help can be adapted for adults with ASD. It will give results on how effective ACT guided self-help is in supporting adults with ASD, to increase psychological flexibility and reduce psychological distress. If guided ACT self-help intervention is effective; this will help increase access and availability of psychological intervention for people with ASD, specifically in relation to associated difficulties in social communication and interaction.

PRIMARY OBJECTIVE To examine whether an ACT bibliotherapy intervention, for adults with a diagnosis of ASD who experience psychological distress, increases psychological flexibility.

SECONDARY OBJECTIVE(S) To examine whether psychological flexibility mediates changes in; personally-identified therapeutic goals, increasing psychological wellbeing and decreasing anxiety, stress and depression.

STUDY DESIGN This is a repeated measures design, using a single case experimental design (SCED). Each participant with be asked to complete weekly measures and shortened measure every three days, please see the outcome measures section for more details of the measures and timeframes. Weekly data collection will last for approximately 10 weeks (baseline and intervention phase), with a two week and four week follow-up.

DATA ANALYSIS SCED data will be predominantly analysed using visual analysis. Data will be plotted onto graphs to analyse the direction of the data (trend), the "magnitude" (level) and the variability of the data (stability). To find out if change from pre and post scores is reliable, a Reliable Change Index (RCI) will be conducted. To determine if any change is clinically significant, a Clinically Significant Criterion (CSC) will be conducted. The data will be analysed at the University of Lincoln and Students home (via secured sites). The data will be analysed using Excel software. No interim analysis is planned for safety, efficacy or management purposes.

Inclusion Criteria:

1. 18+ years old with a formal diagnosis of Autistic Spectrum Disorder, without a diagnosis if an Intellectual Disability.
2. To be over the age of 18 years.
3. Accessing Nottingham City Autism Service
4. Experiencing elevated anxiety, and / or stress, and /or depression and meet the clinical threshold or moderate on the Depression, Anxiety and Stress Scale.
5. Access to the internet via an electronic device (to complete electronic measures).
6. Agreement and knowledge of the time commitment for the completion of the intervention, competition of measure and change questionnaire at the end of the study.

Exclusion Criteria:

1. Unable to communicate fluently in English (justification: the cost of hiring an interpreter).
2. Unable to read English (justification: participant will be unable to read and engage in the bibliotherapy)
3. Adults who are currently accessing psychological therapy. If participants start psychological therapy during the study, they will be removed from the study (justification: unable to separate out effects of research intervention from psychological therapy intervention).
4. If they have a co-morbid diagnosis of intellectual disability (justification: may have different needs regarding therapy adaptations.
5. No access to mobile or internet (justification: unable to complete measures).

1. No individual participant data will be shared with researchers not named in this study.
2. The results of the World Health Organisations Quality of Life Questionnaire (WHOQoL) will be shared anomalously with the World Health Organisation as stipulated by the organisation and specified in the participant consent form.
3. Data collected will be collated and results will be written for publication. All participants will remain autonomous. The target journal identified is The Journal of Contextual and Behavioural Science.