Current global estimates suggest the proportion of the population with autism spectrum disorder (ASD) who have intellectual disability (ID) is approximately 50%. Our objective was to ascertain the existence of selection bias due to under-inclusion of populations with ID across all fields of autism research. A sub-goal was to evaluate inconsistencies in reporting of findings. This review covers all original research published in 2016 in autism-specific journals with an impact factor greater than 3. Across 301 included studies, 100,245 participants had ASD. A random effects meta-analysis was used to estimate the proportion of participants without ID. Selection bias was defined as where more than 75% of participants did not have ID. Meta-analysis estimated 94% of all participants identified as being on the autism spectrum in the studies reviewed did not have ID (95% CI 0.91–0.97). Eight out of ten studies demonstrated selection bias against participants with ID. The reporting of participant characteristics was generally poor: information about participants’ intellectual ability was absent in 38% of studies (n = 114). Where there was selection bias on ID, only 31% of studies mentioned lack of generalisability as a limitation. We found selection bias against ID throughout all fields of autism research. We recommend transparent reporting about ID and strategies for inclusion for this much marginalised group.

中文翻译：

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自闭症研究中智力选择的偏见：横断面研究和荟萃分析。

当前的全球估计表明，患有智能障碍（ID）的自闭症谱系障碍（ASD）人口比例约为50％。我们的目标是确定在自闭症研究的所有领域中归因于ID数量不足的人群的选择偏见的存在。一个子目标是评估报告结果中的不一致之处。该评价涵盖2016年在自闭症特定期刊上发表的所有原始研究，影响因子大于3。在301项纳入研究中，有100,245名参与者患有自闭症。使用随机效应荟萃分析来估计没有ID的参与者的比例。选择偏倚的定义是超过75％的参与者没有ID。荟萃分析估计，在所审查的研究中被确定为自闭症谱系的所有参与者中，有94％没有ID（95％CI 0.91-0.97）。十项研究中有八项显示对ID参与者的选择偏见。参与者特征的报告通常很差：在38％的研究中没有关于参与者智力的信息（n = 114）。如果对ID的选择存在偏见，则只有31％的研究提到缺乏通用性作为限制。我们发现自闭症研究的所有领域对ID的选择都有偏见。我们建议为这个边缘化群体透明地报告ID和包含策略。参与者特征的报告通常很差：在38％的研究中没有关于参与者智力的信息（n = 114）。如果对ID的选择存在偏见，则只有31％的研究提到缺乏通用性作为限制。我们发现自闭症研究的所有领域对ID的选择都有偏见。我们建议为这个边缘化群体透明地报告ID和包含策略。参与者特征的报告通常很差：在38％的研究中没有关于参与者智力的信息（n = 114）。如果对ID的选择存在偏见，则只有31％的研究提到缺乏通用性作为限制。我们发现自闭症研究的所有领域对ID的选择都有偏见。我们建议为这个边缘化群体透明地报告ID和包含策略。