Developing a regression equation for predicting premorbid functioning in an Australian sample using the National Adult Reading Test

Figures & data

Table 1. Demographic characteristics of the non‐impaired and clinical samples

Sample	Variable	Male	Female	Total
Non‐impaired	n	49	62	111
	Age (M (SD))	33.80 (11.71)	30.92 (12.95)	32.19 (12.45)
	Min–Max	18–64	18–60	18–64
	Years of formal education (M (SD))	15.25 (2.60)	15.13 (2.41)	15.18 (2.49)
	Min–Max	9–19	11–21	9–21
Clinical	n	15	7	22
	Age (M (SD))	47.44 (12.39)	53.83 (13.56)	49.18 (12.73)
	Min–Max	30–67	34–69	30–69
	Years of formal education (M (SD))	10.19 (2.29)	11.67 (4.27)	10.59 (2.89)
	Min–Max	6–15	6–16	6–16

Table 2. Obtained scores of the non‐impaired sample on tests of current and premorbid IQ

Test	M	SD	Min–Max
WAIS‐IV	107.33	11.45	75–133
NART	110.78	4.57	99–124
NART‐2	105.25	6.91	87–126
WTAR	105.17	6.44	84–117
TOPF	103.21	10.60	78–128

Note. N = 111.

Table 3. (a) Regression equations for predicting WAIS‐IV index scores using NART/NART‐2 errors and demographics. (b) Regression analysis of WAIS‐IV FSIQ predictors for the regression equations for the non‐clinical sample

WAIS‐IV index prediction (NART/NART‐2 errors alone)	WAIS‐IV index prediction (NART/NART‐2 errors + demographics)
(a)
Predicted VCI = 127.78 − 1.189 * (NART/NART‐2 errors)	Predicted VCI = 126.78 − 1.180 * (NART/NART‐2 errors) − 0.142 * (age) − 0.383 * (sex) + 0.394 * (education)
Predicted PRI = 128.32 − 1.027 * (NART/NART‐2 errors)	Predicted PRI = 124.35 − 0.916 * (NART/NART‐2 errors) − 0.091 * (age) − 3.711 * (sex) + 0.685 * (education)
Predicted WMI = 130.56 − 1.199 * (NART/NART‐2 errors)	Predicted WMI = 124.08–1.013 * (NART/NART‐2 errors) − 0.054 * (age) − 6.059 * (sex) + 0.910 * (education)
Predicted PSI = 120.63 − 0.604 * (NART/NART‐2 errors)	Predicted PSI = 89.81 − 0.519 * (NART/NART‐2 errors) − .091 * (age) + 6.575 * (sex) + 1.428 * (education)
Model	Predictor	β	t	p	r	sr
(b)
1	NART/NART‐2 errors	−.625	−8.36	<.001	−.625	−.625
2	NART/NART‐2 errors	−.571	−7.25	<.001	−.625	−.515
	Age	−.128	−1.63	.106	−.093	−.116
	Sex	−.066	−0.92	.358	−.138	−.065
	Education	.375	2.52	.013	.429	.179

Note. PRI = Perceptual Reasoning Index; PSI = Processing Speed Index; VCI = Verbal Comprehension Index; WMI = Working Memory Index.

Table 4. Regression analysis of VCI, PRI, and WMI predictors for the non‐impaired sample

	Model	Predictor	β	t	p	r	sr
VCI	1	NART/NART‐2 errors	−.616	−8.16	<.001	−.616	−.616
	2	NART/NART‐2 errors	−.611	−7.47	<.001	−.616	−.550
		Age	−.164	−2.01	.047	−.191	−.148
		Sex	−.018	−0.24	.813	−.023	.017
		Education	.091	1.08	.285	.104	.079
PRI	1	NART/NART‐2 errors	−.485	−5.80	<.001	−.485	−.485
	2	NART/NART‐2 errors	−.433	−4.78	<.001	−.485	−.390
		Age	−.096	−1.06	.293	−.053	−.086
		Sex	−.157	−1.89	.061	−.211	−.154
		Education	.144	1.54	.127	.316	.125
WMI	1	NART/NART‐2 errors	−.510	−6.20	<.001	−.510	−.510
	2	NART/NART‐2 errors	−.431	−4.94	<.001	−.510	−.388
		Age	−.051	−.584	.561	−.009	−.046
		Sex	−.230	−2.89	.005	−.290	−.227
		Education	.173	1.91	.059	.331	.150
PSI	1	NART/NART‐2 errors	−.218	−2.33	<.001	−.218	−.218
	2	NART/NART‐2 errors	−.188	5.75	.060	−.218	−.169
		Age	−.074	−1.90	.457	−.141	−.066
		Sex	.212	−0.75	.021	.189	.209
		Education	.230	2.25	.027	.308	.200

Table 5. Injury data for the clinical sample

PTA	GCS	CT/MRI	Time since injury
<24-h	N/A	NAD	1-year 10-months
<24-h	N/A	N/A	15-years 5-months
24-h to 7-days	N/A	Right frontal subdural haematoma.	5-years 5-months
<24-h	15	Depressed skull fracture and removal of small extradural haematoma	1-year 5-months
<24-h	N/A	NAD	3-months
<24-h	N/A	NAD	2-years
<24-h	N/A	Very extensive restricted diffusion involving right temporal lobe and median and inferior aspect. Also small focal area of restricted diffusion involving surface gyri and left gyrus in left temporal region posteriorly. Discrete restricted diffusion also evident involving central aspect of right thalamus	3-years 8-months
<24-h	14	NAD	7-months
<24-h	14	Left subarachnoid haemorrhage, left subdural haemorrhage, left frontal and temporal contusions, as well as fracture of the right petrous temporal bone	1-year 5-months
<24-h	N/A	NAD	5-months
<24-h	N/A	NAD	5-years 2-months
<24-h	N/A	NAD	4-months
<24-h	N/A	NAD	4-months
<24-h	N/A	Two minor non‐specific small T2 hyperintense foci in the white matter of the right frontal lobe.	1-year 9-months
>7-days	N/A	N/A	24-years 5-months
24-h to 7-days	9	Left orbital floor blowout fracture.	6-years
<24-h	15	Acute subdural haemorrhage in frontal lobe with mild cortical atrophy.	2-years
<24-h	N/A	NAD	4-years 2-months
<24-h	N/A	NAD	6-years
<24-h	N/A	NAD	7-years 8-months
24-h to 7-days	N/A	Fracture right mastoid with bleed in the right middle ear, mastoid air cells. No intracranial bleed	2-years 4-months
24-h to 7-days	15	Displaced fracture of the left orbital floor and left zygomatic facial complex but no evidence of craniofacial fracture	5-years 10-months

Note. GCS = PTA = Post‐Traumatic Amnesia, Glasgow Coma Scale, N/A = Not Available, NAD = No abnormality detected.

Table 6. Descriptive statistics of index scores produced by the WAIS‐IV, regression equations, and the TOPF with and without demographic correction for the clinical sample

		Predicted score			Mean difference (WAIS‐IV index—predicted score)	P
	Measure	M	SD	Min–max
FSIQ	WAIS‐IV	82.00	12.65	59–108
	Regression equation (no demographics)	90.21	10.48	71–121	−8.21	.006
	Regression equation (with demographics)	86.35	14.71	61–116	−4.35	.678
	TOPF	85.73	14.48	70–120	−3.73	1.000
	TOPF (with demographics)	91.86	10.48	77–116	−9.86	<.001
VCI	WAIS‐IV	88.91	14.41	63–125
	Regression equation (no demographics)	87.52	13.29	70–116	1.39	1.000
	Regression equation (with demographics)	83.98	13.69	61–112	4.93	.042
	TOPF (equative model)	85.18	15.29	63–119	3.73	.664
	TOPF (with demographics)	90.59	11.14	74–116	−1.68	1.000
PRI	WAIS‐IV	86.73	9.39	73–104
	Regression equation (no demographics)	93.54	11.48	78–118	−6.81	.071
	Regression equation (with demographics)	91.70	11.25	70–113	−4.97	.479
	TOPF (equative model)	86.64	13.67	69–119	−0.09	1.000
	TOPF (with demographics)	96.23	6.65	86–111	−9.50	<.001
WMI	WAIS‐IV	83.77	13.88	63–111
	Regression equation (no demographics)	89.96	13.40	72–119	−6.19	.197
	Regression equation (with demographics)	89.26	12.77	64–114	−5.49	.435
	TOPF (equative model)	87.00	14.12	66–119	−3.23	1.000
	TOPF (with demographics)	93.00	8.53	79–112	−9.23	.005
PSI	WAIS‐IV	79.05	13.75	56–108
	Regression equation (no demographics) FSIQ	100.18	6.75	91–115	−21.13	<.001
	Regression equation (with demographics) FSIQ	92.34	10.24	79–115	−13.29	.002
	TOPF (equative model)	85.95	14.70	65–119	−6.90	.556
	TOPF (with demographics)	94.91	8.02	86–116	−15.86	<.001