Reliability of WISC and WIAT

Essay by sjmillUniversity, Bachelor'sB, September 2011

download word file, 8 pages 0.0

one

Table 1(a).

Calculations of z-scores, percentile ranks and confidence intervals for Ben's WISC-IV scores

Full Scale IQ

Verbal Comprehension

Perceptual Reasoning

Working Memory

Processing Speed

z=99-100/15

z=114-100/15

z=90-100/15

z=83-100/15

z=106-100/15

z*=0.07

z*= 0.93

z*=-0.67

z*=-1.13

z*=0.40

P(%)/R** = 16

P(%)/R** = 83

P(%)/R** =26

P(%)/R** =13

P(%)/R** =66

95%ci=2.60(sem)x1.96

95%ci=3.67(sem)x1.96

95%ci=3.97(sem)x1.96

95%ci=4.24(sem)x1.96

95%ci=4.97(sem)x1.96

95%ci=± 5.096

95%ci=± 7.19

95%ci=± 7.78

95%ci=± 8.31

95%ci=± 9.74

Where * z-score,** percentile rank & 95%ci= confidence intervals

Table 1 (b).

Calculations of z-scores, percentile ranks and confidence intervals for Ben's WIAT-II scores

Word Reading

Numerical Operations

Spelling

Pseudoword Decoding

Maths Reasoning

z=110-100/15

z=85-100/15

z=108-100/15

z=115-100/15

z=74-100/15

z*=0.67

z*= -1.0

z*=0.53

z*=1

z*=-1.73

P(%)/R** =74

P(%)/R** = 83

P(%)/R** =

P(%)/R** =

P(%)/R** =

95%ci=2.12(sem)x1.96

95%ci=4.50(sem)x1.96

95%ci=3.67(sem)x1.96

95%ci=2.60(sem)x1.96

95%ci=3.97(sem)x1.96

95%ci=± 4.15

95%ci=± 8.82

95%ci=± 7.20

95%ci=± 5.1

95%ci=± 7.78

Where * z-score,** percentile rank & 95%ci= confidence intervals

two

If I want to be 95% confident that the two scores are different, I would require them to be separated by two standard errors of the difference.

A separation of only one standard error of the difference would only give me 68% confidence that the two scores are different.

As a result of the workings below I can be, 95% confident that the two scores (verbal comprehension) and (perceptual reasoning) differing by 2Æ¡diff (10.8) represent true score differences.

Table 2.

Methods of calculating the standard error of difference between two scores:

Method one:

Method two:

σdiff= √σ2means1 + σ2means2

σdiff = σ(sd) √2 - r1-r2

σdiff= √13.47+15.76

σdiff = 15 √ 2-0.94-0.93

σdiff= √29.20

σdiff = 15 x 0.13

σdiff = 5.40

σdiff = 5.40

three

In all five individual tests Ben's results were statistically significant (p>0.05). Within the subgroups of word reading, spelling and pseudoword decoding, his scores were significantly above his predicted score. In...