Wechsler Individual Achievement Test

About the measure

Rating Psychometric

Rating Implementation

Subscales

Listening comprehension, oral expression, word reading, reading comprehension, spelling numerical operations and mathematical reasoning NB not all scales available for four year olds

Target construct

Oral language: Listening comprehension Oral expression Literacy: single word reading, reading comprehension, reading speed and spelling. Numeracy: Numerical operations Mathematical reasoning

Test Authors

Wechsler, D.

Publisher

Pearson

Implementation

AgeⓘAge (in years) covered by the survey. Using the measure outside this age range may result in inaccurate information.

4 years to 25 years and 11 months year(s)

Prior knowledge required

Psychologists , speech or occupational therapists, mental health professionals and health practitioners with appropriate Graduate and professional qualifications in their field of practice.

ScoringⓘStandardised: Can easily be summed or averaged Complex: Requires judgement or assessment on behalf of the scorer

Scoring clear and transparent, need to distinguish raw scale standard scores and norms. Writing scales challenging to evaluate

TimeⓘAn estimate of the time (in minutes) taken for an individual to complete one survey

Norm referenced min(s)

Psychometric

UK normsⓘWhether the measure has been calibrated with a UK sample (as opposed to generating psychometric details from a Foreign (e.g. USA) sample).

YES (from 6 years onwards only)

Norm / Criterion referenced

Norm referenced

Standardisation sample

892

ReliabilityⓘWhere observations (e.g. teacher or peer report rather than self report) are used, this measure of reliability indicates how closely related each score is. A higher value suggests a more reliable measure.

Reliability of age-based coefficients ranged 0.90 to 0.97. SEM of composites ranged 2.56 to 4.67. test retest ranged 0.88 to 0.95

Criterion validityⓘAn assessment of how well the measures relates to other, well-validated assessments.

Insufficient data in the public domain to evaluate

Construct validityⓘFurther to the use of CFA and EFA, this reports any details demonstrating how well the measure is seen to represent the conceptual domain it comes from.

Data available for WIAT III ranging from .6 to .82, although this varies between scales

Concurrent validityⓘSimilar to Criterion, this is a measure of how well the measure relates to other similar (or dissimilar) domains, as evidence of its validity.

For reading and spelling WIAT correlated with SAT (0.72, 0.76), ITBS (0.78, 0.53) and CAT (0.84 , 0.74). Inter correlation between subtests was 0.33 and 0.86, and between composites 0.44 and 0.94.