for people ages 21 years and up (full criteria)
healthy people welcome
at San Francisco, California and other locations
study started
estimated completion



We aim to examine whether a purchasing incentive for healthy foods has the same effect on dietary intake in a community with and a community without a purchasing penalty for unhealthy foods. We will perform a randomized non-inferiority trial in two locations, San Francisco (SF) and Los Angeles (LA) to test whether a voucher for purchasing fresh fruits and vegetables has a similar effect in LA and in SF, where the former does not but the latter does have a tax on sugar-sweetened beverages. Participants will be recruited from 4 neighborhoods (N=312) with 2 SF neighborhoods (exposed to the SSB tax) and 2 LA neighborhoods (not exposed to the SSB tax).

Official Title

The EValuating Interventions in Diabetogenic Environments Through Natural Controlled Experiments (EVIDENCE) Trial


We will test the hypothesis that a positive incentive for healthy foods (fresh fruits and vegetables, F&Vs) will be utilized as effectively in a community without a purchasing penalty for unhealthy foods (a sugar-sweetened beverage [SSB] tax) as in a community with a purchasing penalty for unhealthy foods (a SSB tax). Our experiment will test the empirically-driven hypothesis in a real-world setting through a noninferiority design: comparing the impact of F&V vouchers in two counties, one without (Los Angeles) and one with (San Francisco) a SSB tax.

Each study participant will receive four paper vouchers per month for a total of six months. Each of these vouchers can be redeemed for fresh or frozen fruits and vegetables at a number of specified local corner stores, supermarkets, or farmer's markets.

Half of these participants will receive and spend these vouchers in an environment which has implemented a SSB tax (SF); the other half will receive and spend these same vouchers in a non-tax environment (LA).

Each individual participant will be enrolled in the study for a total of seven months from initial orientation and participant consent (M0) to final data collection during final month of intervention (M6).

We are using a non-inferiority trial design. We are aiming to test whether there is a significant difference in total cup-equivalents of F&V intake in LA participants as compared to SF participants when given F&V vouchers. That is, we aim to test whether the F&V voucher is less effective in LA than in SF. This is important to test because it has been purported that SF has a unique food environment with high accessibility to fresh F&V through farmer's markets and a plethora of corner stores, as well as a SSB tax that discourages less healthy foods, potentially leaving more funds for healthier F&Vs. Thus, we aim to determine the change in consumption of F&V in LA participants is non-inferiority to that of SF participants, when both are given F&V vouchers.


Cardiovascular Diseases nutrition fruits and vegetables sugar-sweetened beverages Fruit and vegetable voucher San Francisco Los Angeles


You can join if…

Open to people ages 21 years and up

  1. Understand English sufficiently to provide informed consent;
  2. Provision of signed and dated informed consent form;
  3. Stated willingness to comply with all study procedures and availability for the duration of the study;
  4. Any gender, aged 21 years or older;
  5. Have self-reported income ≤250% of the federal poverty level;
  6. Have regular access to a mobile phone;
  7. Have a safe and secure mailing address at which to receive vouchers;
  8. Be a resident of the Counties of San Francisco or Los Angeles as defined by official municipal boundaries.

You CAN'T join if...

  1. Currently participating in any other dietary or nutrition study that would impact his or her normal eating patterns;
  2. Currently be enrolled in and receiving EatSF, CHIVES, or Vouchers4Veggies vouchers;
  3. Has active diagnosis of cancer or congestive heart failure;
  4. Is planning to move out of San Francisco or Los Angeles in the next 12 months;
  5. Currently pregnant.
  6. Currently live with and share a food budget with a current Vouchers4Veggies, EVIDENCE, or CHIVES study participant.


  • University of California
    San Francisco California 94158 United States
  • Stanford University
    Stanford California 94305 United States


in progress, not accepting new patients
Start Date
Completion Date
Sanjay Basu, MD, PhD
San Francisco program
Los Angeles program
Study Type
Last Updated