Table 1. Single and Multiple Weighted Regression Analyses for MWT and WST Scores.

	k	b	SE	p	R 2
MWT (1971–2007)
Single regression	960				.14
Intercept		95.74	0.81	<.001
Assumed year of study performance		0.37	0.03	<.001
Multiple regression	900				.14
Intercept		96.56	1.35	<.001
Assumed year of study performance		0.37	0.03	<.001
Mean age		−0.02	0.02	.448
WST (1995–2006)
Single regression	164				.03
Intercept		103.17	1.43	<.001
Assumed year of study performance		0.36	0.17	.042
Multiple regression	154				.06
Intercept		100.29	1.89	<.001
Assumed year of study performance		0.20	0.18	.265
Mean age		0.09	0.03	.007

Note. All measures in regression analyses were weighted according to sample size; slopes of assumed year of study performance can be interpreted as average gain per year in IQ points; k denotes number of included samples; b denotes the unstandardized regression coefficients; SE  =  standard error; R ² denotes percentage of variance of data that is explained by the model.