I agree with Julia that studies that link community-level impacts to murals or other public art are hard to come by.  I reviewed a some of the literature available specifically about murals and graffiti abatement here and public art more generally in this report: https://www.lacountyarts.org/sites/default/files/lacac_artasinfrastructure_report_2018_-_web_1.pdf. There are two evaluations of the impact of murals that might be worth looking into that I refer to in the report.  I'm copying my report summaries here:

Two formal evaluations of the Mural Arts Program in Philadelphia indicate some of the potential and difficulties for evaluating public art programs. The first was done as the Mural Arts Program was shifting its location within the city government structure and developing as a separate nonprofit entity. This evaluation, completed by the Social Impact of the Arts Program at the University of Pennsylvania, focused on developing data gathering capacity within Mural Arts and proposed an economic community investment leverage model to talk about the impact of engaging the community in the mural making process. In addition, it was recommended that future evaluations focus on the potential for murals to build social capital and bridge capacity among community members and organizations.

The second evaluation, conducted by Yale University School of Medicine, focused on a partnership between the Mural Arts Program and the Philadelphia Department of Behavorial Health and Intellectual Disability, called Porch Light. In this program, public murals were intended to enhance collective efficacy among residents and the aesthetic quality of the neighborhood so that health risks related to neighborhood decay and disorder would be reduced. Porch Light was also expected to have a positive impact on individual health for people with mental health or substance abuse challenges who were involved in the process of making the murals. The evaluation found that murals changed residents’ perceptions about their neighborhood in terms of collective efficacy and aesthetic quality and perceptions about behavioral health when artworks included behavioral health themes. Evaluators concluded that further research was necessary to determine individual health benefits for program participants. Still, evidence suggested mural-making was positive for individuals and that murals may serve as a catalyst for change and mobilize residents for community action.

Hope this helps!

Best,

Susannah