Table 4.

Hierarchical regression analysis predicting FM 50 kHz USV in response to the seventh day of treatment. Interactions were entered independently, such that interactions were tested then removed from the model. See Table 1’s description for the interpretation of R², β, and t.

	Step and predictor variable	R2	β	t
Step 1		.44**
	IEN		−.24	1.61
	NPP		.02	0.16
	H-USV FM		.62	4.22***
Step 2		.52
	Low 0.3 mg/kg		−.22	1.29
	High 1.0 mg/kg		−.35	1.90
Step 3
	Low 0.3 mg/kg × IEN	.58	−.10	0.46
	High 1.0 mg/kg × IEN		−.31	1.72
	Low 0.3 mg/kg × NPP	.54	−.18	0.94
	High 1.0 mg/kg × NPP		−.35	0.93
	Low 0.3 mg/kg × H-USV FM	.53	.04	0.15
	High 1.0 mg/kg × H-USV FM		.15	0.57
	IEN × NPP	.54	.18	1.02
	IEN × H-USV FM	.63	−.35	2.67**
	NPP × H-USV FM	.52	−.04	0.25

^*p < .05;

^**p < .01;

^***p < .001