Hypothetical Percent of Population Obtaining Differences between VCI

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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 left-most, 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 right-most 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 WISC-IV 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