Table 1.

Study characteristics

First author	Location (city, country)	Study design	Study population	Sample size	Quality assessment	Control/ comparison group	Intervention group	Setting of location of test uptake (clinical or nonclinical)	STI tested	Function of uptake
Chacko [22]	Baltimore, USA	Quasi-experimental interventiona	Teenagers treated at a STI clinic	519	7	Request for a test of cure	CG + incentive of entrance into $50 lottery	Clinical	Gonorrhea	Post-infection test of cure
Currie [27]b	Australia Capital Territory, Australia	Quasi-experimental intervention	Sexually active university students	3652	8	Screening offered at campus activities	$10 incentive for on-campus screening and result retrieval via text message	Non-clinical, on-campus screening	Chlamydia	Screening test
Geringer [23]	Philadelphia, USA	Quasi-experimental intervention	General population	708	7	Testing and result retrieval at homeless shelters and STI centers	CG + $5 incentive for test result retrieval	Clinical and nonclinical Non-clinical, homeless shelters/ soup kitchens	Syphilis	Screening test
Haukoos [25]	Los Angeles, USA	Quasi-experimental intervention	ED patients with a high risk of HIV	372	7	Referral for VCT 1 week after ED visit	CG + $25 incentive for fulfillment of VCT referral	Clinical	HIV	Screening test
Malotte [24]	Prince George’s County and Los Angeles, USA	Randomized controlled trial	Patients treated at a STI clinic	423	8	Request for 3 month retesting	CG + $25 incentive for retesting	Clinical	Gonorrhea, chlamydia	Post-infection repeat test
Nglazi [28]	Cape Town, South Africa	Quasi-experimental intervention	Men in community	8708	7	Use of a mobile VCT service	CG + appointment and $10.30 food voucher	Non-clinical, mobile VCT service	HIV	Screening test
Thornton [26]	Malawi	Randomized controlled trial	Individuals previously tested for STI	2812	7	Request for result retrieval at temporary centers	CG + $1.01 incentive for result retrievalc	Non-clinical, temporary VCT centers within neighbors	HIV	Screening test

CG Control group, VCT voluntary counseling and testing

^aQuasi-experimental study designs intend to estimate the causal impact of an intervention, but without random assignment

^bStudy contained a third non-comparable study group

^cInventive levels were varied at random between 0 and 3 USD