Direct from Google: https://support.google.com/business/answer/7091?hl=en

(Emphasis Added)

Prominence
Prominence is also based on information that Google has about a business from across the web (like links, articles, and directories). Google review count and score are factored into local search ranking: more reviews and positive ratings will probably improve a business’s local ranking.

Manage and respond to reviews
Interact with customers by responding to reviews that they leave about your business. Responding to reviews shows that you value your customers and the feedback that they leave about your business. High-quality, positive reviews from your customers will improve your business’s visibility and increase the likelihood that a potential customer will visit your location. Encourage customers to leave feedback by creating a link they can click to write reviews Prominence is also based on information that Google has about a business from across the web (like links, articles, and directories).