This study may be useful for an economic impact study grant or to research this data in your community. And I might suggest that the bolded sentence in the second paragraph could be used as a way to show farmers markets impact already.

Forty-seven percent of people surveyed said that buying from local and small businesses has the greatest impact on improving life in one’s local area, while 29 percent cited voting in local elections as key, and 20 percent favored volunteering for community organizations. And 53 percent of those surveyed said that their personal resources, like time and money, gave them more ability to make an impact in their local areas. That feeling was particularly strong among people age 39 and younger, according to the polling data.

If Americans prefer grassroots action, then they also see the climate for homegrown solutions improving in small ways: Forty-one percent of people surveyed said that average people had more influence now than they did 10 years ago in bringing about changes in their local areas. Interestingly, women of all ages felt like they had more influence now over local issues than men, of all ages, felt like they had.

Americans Prefer Their Solutions Locally Sourced – CityLab.