What are the guidelines for administering and interpreting standardized Intelligence Quotient (IQ) tests?

Standardized IQ Testing: Guidelines for Administration and Interpretation

Standardized IQ testing must be administered by qualified practitioners (e.g., psychologists) and should always be interpreted alongside clinical assessment and adaptive functioning measures, never in isolation, as a single IQ score is insufficient for understanding an individual's true cognitive abilities. 1

Who Should Administer IQ Tests

• Only qualified practitioners such as psychologists should conduct formal diagnostic evaluations of intellectual functioning 1
• Primary care and mental health professionals should refer children and adolescents with academic performance or behavioral challenges for standardized testing rather than administering tests themselves 1

When to Administer IQ Tests

Age Considerations

• IQ measures are not considered reliable in children under 5 years of age; use the term "Global Developmental Delay" instead for significant limitations in two or more developmental domains 1
• For individuals over age 5 with severe sensory, physical, communicative, or psychiatric impairments that make assessment difficult, use "Unspecified Intellectual Disability" 1

Indications for Testing

• Positive developmental screening results at well-child visits (9,12,18,24,30 months) 1
• Academic performance difficulties or behavioral challenges in school-age children and adolescents 1
• Suspected cognitive impairment based on clinical observation or informant report 1

Critical Interpretation Principles

The IQ Score Alone is Inadequate

The profile of IQ subtests is more clinically useful than the composite IQ score alone, as it reveals both cognitive strengths and weaknesses requiring specific supports. 1, 2

• DSM-5 explicitly states that IQ scores are "approximations of conceptual functioning but may be insufficient to assess reasoning in real life situations and mastery of practical skills" 1
• Individual cognitive profiles based on neuropsychological testing provide more actionable information than a single number 1, 2
• The general intelligence factor (g) explains up to 63% of common variance, but specific factors must also be considered 2

Mandatory Complementary Assessment

Intellectual deficit criteria are met only when confirmed by BOTH clinical assessment AND standardized testing—never by testing alone. 1

• Adaptive functioning must be assessed using validated measures in three domains: conceptual, social, and practical 1
• Adaptive functioning requires clinical assessment because standardized scales do not capture all functional domains 1
• Assessment should consider performance across multiple environments (home, school, work, community) 1

Factors That Compromise Test Validity

Environmental and Personal Factors

Performance on standardized testing can be significantly affected by:

• Motivation, cooperation, interest, and temperament at time of testing 1, 2
• Physical health and mental health status 1, 2
• Test setting characteristics and examiner's supportive attitude 1, 2
• Communication, sensory, and motor limitations 1

Cultural and Linguistic Considerations

Performance is systematically underestimated in children from cultural and linguistic minorities, as testing instruments may lack sensitivity for these populations. 1, 2

• Test selection must account for language and cultural appropriateness 1, 2
• Educational background, occupation, and social activities must inform interpretation 1
• Highest level of education achieved should be recorded and considered when interpreting scores 1

Reliability Limitations

Results are less reliable for individuals with more severe intellectual disability or language impairment, as fewer such individuals were included in standardization samples. 1, 2

• Clinical training and judgment are essential for proper interpretation 1, 2
• Ratio IQ scores (calculated when standard testing cannot be completed) show significant discrepancies from standard scores, especially at distribution extremes, and should be used with extreme caution 3

Reassessment Requirements

Federal law requires re-evaluation at least every 3 years in school-aged children, and continued reassessment is necessary as cognitive impacts can change over time. 1

• Provisional diagnoses may be necessary when reliable testing is not immediately possible 1
• Different equivalent screening forms should be used at transition points to limit practice effects 1
• Reassessment timing should consider evolving pathology, rehabilitation effects, and changing life demands 1

Common Pitfalls to Avoid

• Never diagnose intellectual disability based on IQ score alone without assessing adaptive functioning 1
• Never interpret test scores without considering baseline intellectual functioning, education, and occupation—task performance may represent functional decline even when not scoring in "impaired" range 1
• Never test during acute delirium; defer detailed assessment until delirium resolves 1
• Never ignore the confounding effects of depression, which has a complex relationship with cognition and can mimic cognitive impairment 1
• Never assume interchangeability between different IQ tests—differences of 10+ points occur in 66% of cases when comparing different instruments 4