Table 1 Assessment issues with DS and other intellectual disabilities

Floor effects

Use measures with graded difficulty measures that are error based. The standard scores on many measures do not provide a range at the lower end. Use measures with a low floor or use raw scores controlling for age

Language ability

Focus on tests that are primarily nonverbal, with nonverbal responses, adapt instructions for the population

Assessment variability due to behavior and cooperation

Include careful interview of caregivers (or teachers), experimenter ratings of behavior and cooperation on each test, multiple tests included as a performance check

Sensitivity of the measures to detect effects

Choose measures with continuous normally distributed outcomes; measures should demonstrate concurrent validity and show age-related change. Measures show differences between populations or have been documented to be impaired in the past literature

Flexibility of use

Choose measures that are easily adaptable across cultures, and that can be used in home or lab-based assessment

Applicability across a range of ages

Choose measures with graded levels of difficulty

Reproducibility, lack of validation of measures in populations with developmental disabilities

Use specially validated tests, collect test-retest reliability estimates that are sample-specific