Improving IQ measurement in intellectual disabilities using true deviation from population norms

Table 1 Descriptive statistics for subscales scored using standardized and deviation scores

Subtests	Percent of standard score of 1 (floored)	Percent of raw score of 0	Range of floored raw scores	Scoring method	Mean (SD)	Median	Range	Skew	Kurtosis
			Non-verbal subtests
Fluid reasoning	57.6%	1.0%	0 to 17	Standard	2.97 (2.93)	1.00	12.00	1.44	1.18
				Deviation	0.24 (5.97)	0.55	29.37	−0.17	0.68
Knowledge	54.3%	3.2%	0 to 13	Standard	2.26 (1.80)	1.00	8.00	1.44	1.26
				Deviation	−0.48 (4.51)	0.82	21.27	−0.32	−0.84
Quantitative reasoning	58.5%	11.9%	0 to 13	Standard	2.47 (2.27)	1.00	11.00	1.59	1.86
				Deviation	−0.98 (5.67)	0.25	24.59	−0.25	−0.93
Visual spatial	43.4%	0.3%	0 to 13	Standard	3.87 (3.37)	3.00	14.00	0.99	0.02
				Deviation	2.29 (5.24)	2.50	28.30	−0.22	−0.28
Working memory	56.5%	0.6%	0 to 13	Standard	2.63 (2.40)	1.00	11.00	1.49	1.47
				Deviation	0.15 (5.09)	0.46	23.89	−0.11	−0.79
			Verbal subtests
Fluid reasoning	76.0%	47.1%	0 to 9	Standard	1.75 (1.62)	1.00	8.00	2.44	5.53
				Deviation	−1.68 (4.65)	−1.87	18.66	0.19	−1.00
Knowledge	74.0%	2.9%	0 to 24	Standard	1.59 (1.23)	1.00	7.00	2.44	5.85
				Deviation	−1.27 (3.94)	−0.62	21.41	−0.56	0.07
Quantitative reasoning	50.0%	13.3%	0 to 10	Standard	2.67 (2.12)	2.00	9.00	1.17	0.53
				Deviation	0.26 (4.60)	0.72	21.96	−0.60	−0.13
Visual spatial	73.4%	2.9%	0 to 13	Standard	1.71 (1.46)	1.00	9.00	2.39	5.88
				Deviation	−1.67 (4.19)	−1.49	22.43	−0.10	−0.60
Working memory	83.8%	16.2%	0 to 13	Standard	1.49 (1.35)	1.00	8.00	3.19	10.10
				Deviation	−4.23 (5.98)	−3.60	31.12	−0.49	0.24

ISSN: 1866-1955