Table 1: Summary of included studies.

Author, Year, Location, Reference Total N Enrolled in Study N Screened N Indicated for Diagnostic Assessment N Subjected to Diagnostic Assessment Details of Excluded Individuals Male % Mean Age in Years Description of Inpatient Setting Description of Study Population Method of Screening Method of Autism Diagnosis Diagnostic Criteria Used Prevalence Estimate STROBE Score
Hare et al. (1999), England, [23] 1305 1305 240 215 Patients on trial leave to other placements were excluded. Also, some were excluded from initial screening for administrative reasons of no clinical significance. 96% of the special hospital population was screened. 86% (185/215) of those subjected to diagnostic assessment. Data pertaining to the male % of the 1305 individuals originally screened is not available. 41.8 (Age range 20-77 years) Three secure psychiatric hospitals All adults. Mixture of non-ID and ID patient, though details regarding the relative proportions of each are not provided within the article. Autism Spectrum Disorder in Adults Screening Questionnaire (ASDASQ)1 [26]. Handicaps, Behaviours and Skills (HBS) schedule [27] and case note analysis. ICD-10 [1] 2.4% (31/1305), increased to 4.8% (62/1305) when equivocal cases are taken into account. 15/22
Mandell et al. (2012), USA, [9] 141 141 (though all patients were subjected to diagnostic assessment irrespective of screening score) 141 141 There were 348 residents within the hospital, so only 41% were screened (141/308). Researchers attempted to obtain consent from all residents; 89% of refusal were passive (i.e. patient unable to give consent). Thus, non-capacitous individuals were excluded. 75% (106/141) 52 State psychiatric hospital Civilly committed patient. 32.6% (46/141) patients had ID. Age range not given. Social Responsiveness Scale (SRS) [28]. Four step process: 1- Historical charts and electronic records reviewed; 2 – Diagnostic Interview for Genetics Studies (DIGS) [29] conducted for each patient; 3 – Autism Diagnostic Interview – Revised (ADI-R) [30] completed by research reliable clinicians; 4 – case conference review by two independent teams DSM-IV2 [20] Overall: 9.9% (14/141). ID subgroup: 19.6% (9/46). Non-ID subgroup: 5.3% (5/95). 16/22
Scragg and Shah (1994), England, [22] 392 392 17 17, though 6 refused to be meet the investigator Female patient excluded, on basis that Asperger’s Syndrome is reporter to be much more common in males. 100% (392/392) No data on age of study population, though the study population were adults. Secure psychiatric hospital (Broadmoor, England) Adult males. Unclear whether any patients in the study population had ID (details on IQ are only given for 9 patients whom met criteria for AS, none of whom had an IQ consistent with ID). Examination of case notes Two stages (after initial screening stage): 1 – Screening Schedule for Autistic Behaviour (Part of the HBS interview schedule) [27]; 2 – Interview by the investigator. Gillberg and Gillberg (1989) [31] criteria 1.5% (6/392) (95% CI – 0.6 to 3.3%), increased to 2.3% with the addition of equivocal cases (However, this estimate was for Asperger’s syndrome only, rather than all forms of ASD). 12/22
Shah et al. (1982), England, [24] 761 n/a 761 761 Exclusion of 129 patients, due to being non-mobile – ‘their inability to walk unaided limited the possibility of their showing the behaviour pattern characteristic of classic Kanner’s syndrome.’ 61% (468/761) No data for mean age available. Youngest patients were 16 years of age. Long stay ID hospital3 The entire study population had ID. n/a Disability Assessment Schedule [32] Details not provided within the article. 4% (27 to 34/761). The precise number of participants being diagnosed with ASD is not provided within the article, though they report a prevalence of 4% from a study population of 761. 12/22

1 Not referred to as the ASDASQ within the article itself, as the tool was (at the time of the Hare et al article being published) an unnamed, unpublished screening tool (which was later named the ASDASQ).
2 Confirmed via correspondence with Dr David Mandell.
3 Referred to as a ‘mental handicap hospital’ within the source article.