This was an open feasibility study in a clinical outpatient context using a mixed-methods approach (i.e., both qualitative and quantitative methods), including adults with ASD and their close relations. The study was approved by the Regional Ethics Committee in Stockholm (2017/1065–31/1). All participants with ASD as well as the participating close relations gave their written informed consent before inclusion in the study. The study adhered to the CONSORT 2010 Checklist and was registered at Clinicaltrials.org (NCT04460976).

Prisma was developed by a group of experienced clinicians with different health care professions from outpatient clinics (two of the authors were coordinating the group: NH, AB). Prisma was primarily designed to be the first intervention after the establishment of an ASD diagnosis at any age in adulthood, and for young adults transitioning into adult services. The aspiration was to make Prisma into an accessible intervention for intellectually able (defined as not having intellectual disability) adults with ASD in outpatient services, and their close relations. The goal is to increase knowledge about autism, as well as provide information on how to access further services. Another important aspect is to enhance active participation and increase relevance for each individual by providing opportunities to ask questions and reflect on individual needs, as well as meet peers with similar experiences.

Prisma is a group-based face-to-face intervention that can be administered by health care professionals with experience of adults with ASD by following the Prisma manual. One to two clinicians (group/course leaders) give the intervention at the clinic and each session is administered by use of a digital slide show with detailed group leader instructions. Participants receive a personal workbook including supporting instructions and spaces to make notes. The structured mapping of own needs in relation to the general session content is registered at the end of each session, using a work sheet included in the workbook. The intervention consists of four weekly 2-h sessions (including breaks, time for questions, and structured mapping of individual needs). For descriptions of content, themes, and focus of the four Prisma sessions, see Table 1.

To increase treatment fidelity, a half-day training course, including an introduction to the intervention and course contents were given to course leaders. Also, course leaders received on-going support from project coordinators (via email, digital platform, telephone, or visits at the respective clinic/center) throughout the study, regarding all issues related to the intervention as well as the course leader’s role. All study and intervention materials were thoroughly structured and made available to the course leaders via a digital platform. Furthermore, the course leaders had access to a manual containing all the parts that were included in the course leader training, answers to FAQs, a structured checklist for time planning, and ready-made suggestions for administration.

Information about how to participate in Prisma was given to patients at each clinic through information brochures in the waiting rooms and/or by clinicians. All patients that expressed interest in participation were contacted by one of the course leaders. A structured screening interview including information about the content of Prisma, as well as a brief assessment of inclusion and exclusion criteria, was conducted by telephone or at the clinic. Individuals who fulfilled the requirements were invited to an information meeting with their close relations where they received more information about the intervention, gave consent for participation, and completed the baseline measurement. An additional individual and final ascertainment of eligibility was performed with each patient and his or her close relations to ensure that the prerequisites for participation were met. The eligibility was based on follow-up on screening interview and relevant questionnaires (The Hospital Anxiety and Depression Scale [HADS]), the patient's own description of his or her current situation and medical records.

The data collection was conducted in 2017 at eight adult outpatient psychiatric clinics and four habilitation clinicsFootnote 1 in the Stockholm area. In total, 13 groups received the psychoeducational intervention Prisma. Each group included approximately 10–15 participants (M = 13 for this study) with ASD and 1–2 close relations per participant.

For inclusion, patients had to meet DSM-IV and/or DSM 5 criteria for ASD and/or ICD-10 criteria for one of the ASD diagnoses under F84, assessed within the Swedish health care system before the study participation. Both patients and the close relations had to be 18 years or older. Sufficient knowledge of the Swedish language was required to understand the course contents. Close relations could be a parent, sibling, partner, friend, or whomever the participant with ASD thought of as a close relation. Having ASD or other diagnoses were not considered exclusion criteria for close relations.

Exclusion criteria for the participants with ASD were not being able to participate with a close relation, intellectual disability, mental or psychosocial instability to a degree that made participation impossible as judged by the course leader or experienced health care professionals (i.e. severe psychiatric comorbidity such as ongoing substance use disorder, manic episodes, psychosis, and acute suicidality). Further reasons for exclusion were the inability to participate in a group, or severe life situations (e.g. homelessness). Parallel treatments and interventions like pharmacological or occupational therapy were not an exclusion criterion. No changes in inclusion and exclusion criteria were made during the study.

Case histories and sociodemographic data for participants with ASD were extracted from medical records. The participants also completed a questionnaire “Current Life Situation Form” covering demographic information and current stressors in different areas of life [24]. A modified version of this questionnaire was used to assess demographic characteristics of the close relation. ASD symptoms were measured using the Ritvo Autism Asperger Diagnostic Scale-14 screen (RAADS-14) [25]. Background and demographic data are described in Table 2 for adults with ASD and in Table 3 for close relations.

Treatment completion was a central outcome for evaluating if Prisma would be a feasible intervention in a clinical setting for adults with ASD and their significant others. Moreover, since adults with ASD were not part of the group that developed Prisma, an important goal for this study was to gather feedback and experiences (treatment acceptability) from participants with ASD and their close relations to further develop Prisma. Outcome measures were gathered through self-ratings before, during, and after Prisma. In addition, for preliminary estimation of treatment effects, self-rating questionnaires were administered at baseline, i.e. 1–2 weeks before the intervention started, and post-intervention, i.e. 1–2 weeks after the last session.

Treatment completion was defined as the proportion of participants who completed the intervention. To be regarded as a completer, the participant had to attend at least 3 out of 4 course sessions.

Acceptability was addressed by measuring credibility, satisfaction, and safety. Treatment credibility was measured with an adjusted version of the Treatment Credibility Scale (TCS) [26]. TCS was administered at baseline (Cronbach’s alfa 0.81, n = 138) and after the last session to participants and course leaders. The TCS includes five items in a 10-point visual analogous scale (VAS). High values indicate high credibility. Treatment satisfaction was evaluated after each session and after the intervention was completed. The Session Evaluation Form (SEF) is a modified version of the Evaluation Questionnaire [19, 27]. SEF consists of five statements rated 0–4 on a Likert scale. Three of the statements target the respondent’s appraisal of the content of the specific lecture. The other two assess the participant’s experience of taking part in group discussions/exchange of experiences and could also be answered “not applicable” if the participant did not share or discuss experiences. At the end of each form, the participants could write comments about the session.

A modified 12-item version of the Patient Evaluation Form (PEF) [28] was distributed at the end of the last session regarding the participant appraisal of the course as a whole. Six items are scored on a Likert scale ranging from 0–4 (Cronbach’s alfa 0.78, n = 132). Four items are open-ended questions for participants to further develop their answers (“How did the intervention help me?”; “How can the intervention improve?”; “What could I have done differently?”; “Is there anything else you want to share about the intervention?”). For the open-ended questions in the PEF, a qualitative thematic analysis was performed [29]. As the non-completers only participated to a limited extent and did not assess the full content of the intervention, only data from completers were included in the main thematic analysis. However, a separate analysis was conducted on non-completers. As participants who answered the open-ended questions at times gave more than one answer, the percentage in Table 6 reflects the proportion of answers rather than individuals. To be considered a theme, a minimum of four similar answers had to be present. One of the authors (DS) analyzed and categorized the answers in themes and another author (NH) confirmed them. The agreement was very high and the few deviating analyses were discussed and placed in the theme’s authors agreed upon. Yet another author (TH) reviewed and confirmed the categorizations. After a consensus discussion with all three researchers (NH, DS, TH), slight changes were made to the description of the themes to clarify what they reflected.

Adverse events were defined as spontaneous oral complaints or instances when patients stated that they experienced negative or unwanted effects during the intervention period. Serious adverse events were defined as events that involved hospital care/hospitalization, due to the intervention. Adverse events and serious adverse events were recorded in the case report form (CRF) folder, and it was judged by the research group if these were associated with the intervention.

All scales that measure preliminary effectiveness were administrated to participants before and after the intervention except for the Burden Assessment Scale (BAS) [30] which was only filled in by close relations.

Acquired knowledge of ASD and support and services was measured using the ASD 20 Questions (Additional file 1). ASD 20 Questions is a knowledge quiz with 20 true/false/don’t know scored items created for this study. High values indicate more acquired knowledge. Moreover, a separate question was included where participants were asked to list all support and treatment interventions helpful for adults with ASD and their close relations. Similar knowledge quizzes have been used in previous studies [15, 27]. Internal consistency of the quiz using Kruder-Richardson 20, at pre-intervention was 0.78 (n = 138).

Relationship quality was measured both from the perspective of the participant with ASD and the close relation with The Questions About Family Members (QAFM) [31]. The QAFM comprises four subscales: (1) Critical Remarks Cronbach’s alfa pre-intervention 0.86 (n = 131) (2) Emotional Over-involvement Cronbach’s alfa pre-intervention 0.74 (n = 132) (3) Perceived Criticism Cronbach’s alfa pre-intervention 0.51 (n = 132) and (4) Perceived Emotional Involvement Cronbach’s alfa pre-intervention 0.43 (n = 135). The scale contains 30 items, which are scored on a 5-point Likert scale. Low scores on the first three subscales, and high scores on the fourth subscale, are indicative of a good quality of relationship.

Mental health. The Hospital Anxiety and Depression Scale (HADS) [32] was used to measure mental health on the two subscales: “depression” Cronbach’s alfa pre-intervention 0.84 (n = 139) and “anxiety” Cronbach’s alfa pre-intervention 0.88 (n = 138). The subscales contain seven items each and were scored on a 0–3 Likert scale with a maximum score of 21 points. Higher scores indicate high symptoms of anxiety and/or depression. Furthermore, two items from the PEF covering participants’ well-being before and after the intervention on a Likert scale of 1–10 (“How would you rate your well-being before the intervention?”, “How would you rate your current well-being”) was used to measure general well-being. High values indicate high well-being.

Quality of life was measured using the Satisfaction With Life Scale (SWLS) [33]. SWLS contains five items, scored on a 7-point Likert scale Cronbach’s alfa pre-intervention 0.91 (n = 139). High values indicate higher satisfaction with life.

Acceptance of diagnosis was measured using adapted version of the Acceptance and Action Questionnaire – II [34], “What I think about my diagnosis” for adults with ASD and “What I think about my close relation’s diagnosis” for close relations. Cronbach’s alfa at pre-intervention was 0.86 for participants with ASD (n = 68) and 0.87 (n = 68) close relations about the adult with ASD’s diagnosis. Both questionnaires contain 7 items, scored on a 7-point Likert scale where lower values indicate higher acceptance.

The burden of care on close relations was assessed using the Burden Assessment Scale (BAS) [30] consisting of 19 items scored on a 4-point Likert scale Cronbach’s alfa at pre-intervention 0.87 (n = 68). High values indicate a greater burden. BAS was used to measure to what extent the close relations experienced a subjective (e.g. emotional distress) and objective (e.g. economic consequences) burden of care.

Statistical outliers in all outcome measures were screened using boxplots in SPSS version 27. The few extreme outliers (1st/3rd Quartile ± 1,5) that were identified did not significantly affect the results and were therefore retained in the subsequent analyses. Outcome data were approximately normally distributed. The main statistical analyses regarding feasibility and efficacy-related measures were performed on all participants attending at least 3 out of 4 sessions and who had completed pre- (T1) and post-measurement (T2).

Comparisons between completers and non-completers were performed on baseline data using unpaired t-tests, Fisher’s exact test, and Pearson’s chi-squared test to detect possible predictors of drop-outs. Unpaired t-tests were used to examine differences post Prisma between individuals with ASD and close relations on the SEF and the PEF. Paired t-tests (pre and post) were used to test preliminary efficacy both for individuals with ASD and the close relations for all outcomes. The effect size was interpreted according to Cohens d: 0.2 = small effect size, 0.5 = medium effect size and 0.8 = large effect size [35].