Table 2.

Mean Full Scale IQ differences across age category and ability classification

Age group	Mean difference	SD	Classification	Canadian norms		American norms
				Mean difference	SD	Mean difference	SD
18–19	8.22	2.18	Extremely Low	9.06	1.82	8.89	2.33
20–24	8.41	2.07	Borderline	8.30	1.51	8.85	1.76
25–29	8.51	2.17	Low Average	7.78	2.23	7.85	1.97
30–34	7.94	2.09	Average (Low)	6.19	1.99	7.54	2.37
35–44	6.86	2.11	Average (High)	3.60	1.91	5.83	2.43
45–54	4.58	2.16	High Average+	3.64	1.91	3.61	1.67
55–64	4.50	2.84

Note: Mean difference is shown for classification based on Full Scale IQ scores calculated using both Canadian and American normative data, as classification is dependent on IQ score.