Table 2.

Associations among study variables over time.

	Baseline			6-Month follow-up			12-Month follow-up
	Heavy drinking days	Marijuana days	PPSI	Heavy drinking days	Marijuana days	PPSI	Heavy drinking days	Marijuana days	PPSI
Baseline
Heavy drinking days	1
	109
Marijuana days	0.14	1
	109	109
PPSI	0.45*	0.17†	1
	109	109	109
6-Month follow-up
Heavy drinking days	0.65*	0.25*	0.45*	1
	90	90	90	90
Marijuana days	0.31*	0.72*	0.32*	0.44*	1
	90	90	90	90	90
PPSI	0.44*	0.26*	0.45*	0.56*	0.39*	1
	89	89	89	89	89	89
1-Year follow-up
Heavy drinking days	0.49*	0.22*	0.40*	0.83*	0.36*	0.52*	1
	86	86	86	86	86	85	86
Marijuana days	0.23*	0.70*	0.25*	0.40*	0.86*	0.32*	0.37*	1
	86	86	86	86	86	85	86	86
PPSI	0.29*	0.36*	0.42*	0.46*	0.37*	0.54*	0.49*	0.43*	1
	85	85	85	85	85	84	85	85	85

Abbreviations: PPSI, perceived peer substance involvement.

Pearson correlation is presented on the top row and N on the bottom.

^*P < .05; ^†P < .10.