Table 5. Hierarchical Linear Regression Analysis of the Effect of Sex, COMT and N-Back Level on N-Back Reaction Time (RT). The Main Effect of Sex, Linear Effect of COMT and Quadratic Effect of COMT were Entered in Block 1, and the Interactions Between Sex and COMT Were Added in Block 2. We Took a Repeated-measures Approach, First Predicting the Average of the 2-Back and 3-Back Levels (Yielding the Main Effects of Sex and COMT), Then Difference Between the 2-Back and 3-Back Levels (Yielding the Interactions Between N-Back, Sex and COMT).

Dependent variable	Predictor	B (SE)	F (omnibus effects) or t-test	P-value
RT average
	Block 1
	Sex	−3.48 (8.55)	t(2486)=0.42	0.67
	COMT		F(2, 2486)=0.29	0.75
	Linear planned comparison	−4.05 (12.14)	t(2486)=0.33	0.74
	Quadratic planned comparison	−7.58 (11.33)	t(2486)=0.67	0.50
	Block 2
	Sex	−5.51 (9.06)	t(2484)=0.61	0.54
	COMT		F(2, 2484)=0.44	0.65
	Linear planned comparison	−5.68 (12.19)	t(2484)=0.47	0.64
	Quadratic planned comparison	−8.97 (11.42)	t(2484)=0.79	0.43
	Sex × COMT		F(2, 2484)=1.30	0.27
	Linear planned comparison	32.17 (24.39)	t(2484)=1.32	0.19
	Quadratic planned comparison	19.81 (22.84)	t(2484)=0.87	0.39
RT difference
	Block 1
	N-Back	33.54 (4.37)	t(2486)=7.67	<0.001
	Sex × N-Back	−36.92 (8.74)	t(2486)=4.22	<0.001
	COMT × N-Back		F(2, 2486)=0.03	0.97
	Linear planned comparison	0.88 (12.41)	t(2486)=0.07	0.94
	Quadratic planned comparison	2.86 (11.59)	t(2486)=0.25	0.81
	Block 2
	N-Back	33.25 (4.64)	t(2484)=7.17	<0.001
	Sex × N-Back	−37.73 (9.27)	t(2484)=4.07	<0.001
	COMT × N-Back		F(2, 2484)=0.02	0.98
	Linear planned comparison	−0.82 (12.47)	t(2484)=0.07	0.95
	Quadratic planned comparison	2.05 (11.68)	t(2484)=0.18	0.86
	Sex × COMT × N-Back		F(2, 2484)=1.09	0.34
	Linear planned comparison	34.59 (24.94)	t(2484)=1.39	0.17
	Quadratic planned comparison	10.24 (23.36)	t(2484)=0.44	0.66

Abbreviations: COMT, catechol-O-ethyltransferase; RT, reaction time.