Table I.

Terms tested in analysis of diffusion and contamination. Negative control terms are terms to which no volunteers were directly exposed. Positive control terms were terms to which all volunteers should have been directly exposed. Test terms were those to which only index participants in the intervention arm were directly exposed.

	Term
	Negative Control	Positive Control	Test
Philadelphia	EXPLORE Matrix method SCHARP	Harm reduction	Peer mentor SPEAKK Injection risk ladder Project FAST Ribbon game Sex risk ladder Freeze frame
Chiang Mai	EXPLORE Project FAST SCHARP data collection and analysis center	A friend who helps friends Harm reduction	6 communication skills (for a friend who helps friends) Ribbon game Cleaning 1×1×1 (1× water, 1× bleach, 1× water) Share the portion of heroin powder Time out role play