A review of the reliability and validity of Likert-type scales for people with intellectual disability.
Likert self-report is safe only for borderline-mild ID when you add pictures, one-word anchors, pretests, and clarifying probes.
01Research in Context
What this study did
Lecavalier et al. (2006) hunted every paper that tested Likert-type scales in people with intellectual disability.
They kept only studies that reported reliability or validity numbers.
The final pool covered adolescents and adults across all ID levels.
What they found
Likert scales give clean data only for borderline to mild ID.
To get that clean data you must add pictures, one-word anchors, a quick pretest, and clarifying questions.
For moderate to profound ID the same scales break down; answers become guesswork.
How this fits with other research
Hatton et al. (2005) showed a pictorial self-competence scale works in children with mild ID.
That single study is one brick in the wall the review builds: pictures plus mild ID equals trustable numbers.
Laugeson et al. (2014) went further, proving proxy tools like the San Martín Scale are needed once severity reaches profound levels.
Together the papers draw a bright line: self-report Likerts stop at mild ID; proxy or interview tools take over after that.
Why it matters
Stop handing five-point smiley-face sheets to every client. Use them only after you check IQ range and add the four design fixes. For moderate or profound ID switch to caregiver scales or structured interviews. This small shift saves you from phantom data and protects treatment decisions.
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02At a glance
03Original abstract
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.
Journal of intellectual disability research : JIDR, 2006 · doi:10.1111/j.1365-2788.2006.00844.x