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Posted 8th March, 2011 by Melanie Knight

 

Significance level .05 .01
Differences between subtest scores  for 13 to 18 years old
Diamonds and Matrices 15 – 18 19 or above
Vocabulary and Verbal analogies 17 – 22 23  or above
Differences between subtests for 19 years and older
Diamonds and Matrices 12 -15 16 or above
Vocabulary and Verbal analogies 14 -18 19 or above

Adapted from table 6.6 from the WRIT Manual (Glutting, Adams and Sheslow, 2000, p.76)

To calculate a learner’s visual and verbal aptitude it is necessary to add the standard scores of the 2 subtests within each domain.  For example to calculate a learner’s visual aptitude score you must add the standard scores for the matrices and diamond subtests together.

However some learners may score significantly better on one subtest than another within a domain.  This poses the question to assessors “Is it safe to combine the learner’s subtest scores to generate a domain score?”

On page 76 of the WRIT manual relevant differences between subtest scores for statistical significance are provided. The differences are listed at 2 levels of statistical significance; p<.05 and p<.01. “P” is an estimate of the probability that the result has occurred by accident.  Therefore the smaller the value of “P”, the greater the statistical significance.  Differences at the .01 level would normally be considered significant by statisticians.

Caution may need to be employed in interpreting domain standard scores when significant differences are found between subtest standard scores ” (WRIT Manual  page 50). However they do not clarify whether it is safe to combine the scores at either the .05 or the .01 level to generate a domain score. Hence it appears to be left to the assessor’s discretion to decide whether to combine statistically significant subtest scores and to comment on the statistically interesting difference.

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