Table 1. Comparison of the younger and older adults on a set of control variables.

	young	old	Mann-Whitney-U
Digit Symbol	64.5 (13.2)	46. 1 (12.7)	U(18,16)  = 54, p<.01
Vocabulary	23.8 (3.4)	21.7 (4.3)	U(18,18)  = 122, p>.2
Mental Rotation	11.3 (3.5)	8.1 (2.8)	U(18,18)  = 87.5, p<.05
Aiming: duration	7.9 (1.8)	10.1 (2.2)	U(11,16)  = 35, p<.01
Aiming: errors	0.9 (2.2)	0.6 (1.3)	U(11,16)  = 82, p>.7
Pegboard: duration	35.2 (3.2)	40.2 (6.5)	U(11,16)  = 50, p<.1
Tracing: errors	17.7 (5.6)	23.9 (7.6)	U(11,16)  = 45, p<.05
Tracing: duration	34.6 (7.8)	28.5 (6.1)	U(11,16)  = 46, p<.05
Tapping: # of taps	202.5 (15.4)	198.4 (15.3)	U(11,16)  = 67, p>.2

For each group the means and the standard deviations (in brackets) are given, and for each variable the result of a Mann-Whitney U-test (durations are in s). In the cognitive tasks, higher values indicate better performance.