WJ cluster diff

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WJ-R Frequency Table: Cluster Differences

Required Difference Between Single Cluster Scores and Mean Cluster Score at 5% Level of Statistical Significance and Frequencies of Such Differences
	Average of 7 Clusters
		Significance Level	Cumulative %
Cluster		.05	1%	2%	5%	10%	15%	20%	25%
Long-term retrieval		9.40	42	38	31	25	22	19	17
Short-term memory		13.03	39	35	28	24	21	18	16
Processing Speed		13.51	35	32	27	22	19	17	16
Auditory Processing		12.20	43	40	33	28	24	22	19
Visual Processing		15.85	48	44	37	31	27	23	21
Comprehension Knowledge		9.94	34	31	26	21	18	16	14
Fluid Reasoning		9.28	40	37	30	26	22	19	17

Note: The differences required for statistical significance are based on the average standard errors of measurement across all ages and calculated with the following formula provided by Davis (1959): Difference score = Z SQRT[(SEmt^2)/K^2+[(K-2)/K](SEmi^2)], where Z is the normal curve value associated with the desired significance level derived with the Bonferroni correction for multiple comparisons, K is the number of tests in the comparison, SEmt^2 is the sum of the squared standard errors of measurement for all tests in the comparison, and SEmi^2 is the squared standard error of measurement for the test of interest.

John and Ron thank Dr. Woodcock for his very generous granting of access to portions of the WJ-R standardization data and for his kind permission to post these tables.

Woodcock, R. W., & Mather, N. (1989). WJ-R Tests of Cognitive Ability --Standard and Supplemental Batteries: Examiner's Manual. In R. W. Woodcock & M. B. Johnson, Woodcock-Johnson Psycho-Educational Battery--Revised. Chicago: Riverside Publishing Co. All rights reserved.