Authors conducted a meta-analysis of diagnostic studies for language impairment in bilingual children and found a serious lack of necessary psychometric measures in the vast majority of studies examined.
Validity refers to the degree to which an item is measuring what it’s actually supposed to be measuring.
Even though standardized test scores should not be used to determine or diagnose disability, quantification is required to demonstrate that a child should receive services. It is the evaluator’s job to use his or her clinical judgement to determine percentage of delay if it exists.
Reliability is the degree of consistency of measurement in a test. A test has a high degree of reliability if it produces similar results consistently under similar conditions.