Background Likert-type scales are increasingly being used among people with intellectual disability (ID). These scales offer an efficient method for capturing a wide range of variance in self-reported attitudes and behaviours. This review is an attempt to evaluate the reliability and validity of Likert-type scales in people with ID.
Methods Fifty-one studies reporting response rates, response bias, reliability and validity of Likert-type scales among adolescents and adults with ID were reviewed.
Results Low response rates were found among adolescents and adults with moderate to profound ID, when pictorial representations of response alternatives were not employed, and for Likert-type scales with self-descriptive statements. Response bias was evident, particularly among adolescents and adults with moderate to profound ID. Likert-type scales have better reliability and validity among adolescents and adults with borderline IQ or mild ID. Pretests and clarifying questions increase reliability and validity.
Conclusions Likert-type scales should include pictorial representations of response alternatives, a single set of one or two word response descriptors, clarifying questions, and pretests, and are best used with adolescents and adults with borderline IQ to mild ID.