Appendix Table A2.

Testing the balance of observables across incentive offers^a

	(1) Random monthly incentive offer (α1)	(2) Bargaining monthly incentive offer (α2)	(3) Random quarterly incentive offer (α3)	(4) Bargaining quarterly incentive offer (α4)
Age (in years)	0.0042	0.0986	0.0127	0.0466
	[0.0444]	[0.0538]+	[0.1332]	[0.1909]
Has HIV or STIb	−0.0009	1.1611	−0.0026	1.0348
	[0.3255]	[0.3956]**	[0.9766]	[1.6794]
Any condom use at last sexual actb,c	−0.2149	0.0239	−0.6447	−1.9480
	[0.3066]	[0.4097]	[0.9198]	[1.7390]
Male sex partners (last month)	−0.0025	−0.0150	−0.0076	−0.0958
	[0.0124]	[0.0234]	[0.0372]	[0.0449]*
Last sex with someone just metc	0.0495	−0.5031	0.1484	−0.0454
	[0.2010]	[0.2587]+	[0.6030]	[0.9773]
Has a stable partnerb	0.1083	0.2501	0.3249	−0.2354
	[0.2067]	[0.2664]	[0.6202]	[1.0207]
Sex workerb	−0.5113	−0.0329	−1.5339	−2.5095
	[0.3560]	[0.4870]	[1.0680]	[1.1144]*
Studentb	−0.0160	0.0170	−0.0479	−0.8064
	[0.2126]	[0.2556]	[0.6377]	[0.9912]
Highest level of educationc	0.2344	0.6055	0.7031	1.4872
	[0.1787]	[0.2137]**	[0.5362]	[0.8940]+
Has correct knowledgeb,f	−0.2326	−0.4491	−0.6977	−0.6633
	[0.2539]	[0.2994]	[0.7617]	[1.2009]
Wealth indexe	0.1586	0.1500	0.4759	1.6207
	[0.1429]	[0.1760]	[0.4287]	[0.7414]*
Constant	4.0089	1.4348	12.0268	11.0874
	[0.9790]**	[1.2247]	[2.9369]**	[4.7299]*
Observations	900	900	900	900
R-squared	0.011	0.042	0.011	0.025

Notes: Table presents results from linear regression where dependent variables were the conditional incentive offers in USD.

Robust standard errors in brackets:

^**p<0.01,

^*p<0.05,

⁺p<0.1

^aThe analytical sample consists of men who have sex with men (MSM), including male sex workers (MSW) with the relevant covariates. MSM defined as a man who has had sex with another man with anal penetration within the last year. The conditional incentive offers were random offers for α1 and α3. The incentive offers for α2, and α 4 were follow-up questions: a bargaining experimental game to increase participation and/or reduce program costs by increasing the incentive offer (for those who initially said “no”) or to lower the incentive offer (for those who initially said “yes”). Conditional incentive offer amounts are expressed in US dollars (USD) of 2008. Data collection took place during October 1-December 15, 2008 in Mexico City; the average exchange rate was 12.97 pesos per USD [29]

^bBinary variable.

^cAny condom use refers to use of condoms by respondent or male partner during last anal sex.

^dEducational levels were: Primary =1; Middle School=2; High School=3; College=4; Graduate=5.

^eThe wealth index was constructed using data on availability of: vehicle, own house, more than five rooms in the house, laptop and desktop computers, cable television, Internet access, and household help.

^fCorrect knowledge (yes/no) was based on a battery of questions about HIV and sexually transmitted infections (STIs).