The ratio is a useful metric allowing people to estimate how many copies a game has sold. In 2018, Jake Birkett, head of Grey Alien Games, calculated that every Steam review could mean between 30 and 150 copies sold.
Since then, however, the ratio has likely changed, especially now that Steam prompts users to leave a review. Additionally, certain Steam sales might have boosted the review activity by giving users rewards.
To find out the current Steam reviews/sales ratio, Carless is calling on studios that have a game available on Steam to anonymously fill out a mini-survey before the end of Friday, July 24th (in your local timezone). The survey needs to be filled out separately for each game available on the store.
The results will be posted in early August.