Hypothetical Percent of
Population Obtaining Differences between VCI, PRI
and FSIQ scores



VCI vs FSIQ 

PRI vs FSIQ 













50 

5.67 

5.48 

25 


25 

9.45 

9.13 

12.5 


20 

10.52 

10.16 

10 


10 

13.56 

13.10 

5 


5 

16.10 

15.56 

2.5 


2 

19.14 

18.49 

1 


1 

21.20 

20.48 

.5 


.1 

27.11 

26.19 

.05 










To use this table:
Find the discrepancy that is just less than the one obtained by the
examinee. The leftmost, bold column gives, in the same row, the percentage of
the population obtaining discrepancies as large as or larger than the located
discrepancy. [If you are interested only in discrepancies in one direction,
e.g., only VCI higher than FSIQ, use the bold percentages in the rightmost
column.]
A VCI  FSIQ discrepancy of 15 points would be found in approximately 5% to
10% of the population (16.10 = 5%; 13.56 = 10%).
The method used to compute the discrepancy between scales that reflect the
percentage of the population obtaining the discrepancy is:
Discrepancy = SD * z * squareroot(2  2*rxy)
Discrepancy = standard deviation of the tests times the selected z value
times the square root of two minus twice the correlation between the two tests.
For example, the discrepancy between the WISCIV VCI and FSIQ that represents
5% of the population (z = 1.96) is:
15 * (1.96) * square root(2  2*0.85) =
15 * 1.96 * square root (2  1.7) =
29.4 * squareroot(0.3) =
29.4 * 0.55 =
16.1
