Ratio IQs (mental age ÷ chronological age × 100) create interpretation problems, especially for adults, because mental age does not increase steadily across the lifespan. Modern intelligence testing instead uses deviation IQs, which:

Compare an individual’s performance to that of their age-based normative group.

Use a fixed mean (typically 100) and standard deviation (often 15 or 16) to express how far above or below the average a person’s score falls.

Option B best captures this idea: deviation IQs are derived from standardized norms with designated means and standard deviations, which are similar across many commonly used IQ tests, allowing for more meaningful interpretation.

The other options do not describe the purpose of deviation IQs:

A. Lower the standard deviation among test takers – deviation IQs standardize the distribution; they don’t simply “lower” the standard deviation.

C. Place primary emphasis on selecting students in extreme intelligence categories – extremes can be identified, but that is not the primary reason deviation IQs were developed.

D. Reflect that all new IQ tests are being based on a common theory of intelligence – tests differ in their theoretical foundations; deviation scoring is a psychometric method, not a theory of intelligence.

Within the Intake, Assessment and Diagnosis area, counselors are expected to understand basic principles of standardized testing, including the interpretation of IQ scores using norm-referenced, deviation-based metrics.