1.5.2 Intelligence testing and cultural context

How scores are produced

• Standardisation means the test is given and scored in a fixed way.

• Norms compare a person's performance with an appropriate reference population.

• Deviation intelligence quotient (IQ) compares performance with people of the same age. Most scales in common use have a mean of 100 and a standard deviation of 15.

• Ratio IQ was the historical method: mental age divided by chronological age, multiplied by 100. Modern adult scores do not use it.

Reliability and validity

• Reliability is about consistency. Every score has some measurement error, so read it with its confidence interval.

• Validity is about whether the evidence supports how you intend to interpret the score, including its links with other measures and relevant outcomes.

• A single total score can hide an uneven profile. Interpret it alongside the history, the person's functioning and the question the assessment is meant to answer.

Culture and opportunity

• Cultural context shapes which skills are valued, educational opportunities, how familiar the tasks are and what test instructions are taken to mean.

• Assess language and sensory needs before testing. Changing the standard administration to meet them can limit comparison with published norms.

• Group averages do not determine an individual's abilities. A difference in scores does not by itself show that the explanation is genetic.

Worked example

1. Convert the position into scale units: 1 × 15 = 15.

2. Add the scale mean: 100 + 15 = 115.

3. Read 115 as relative standing on that scale. It is not a percentage of intelligence or a fixed personal limit.

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