I’m sure there is in fact such a study
It’s easy to calculate. You can do it yourself. Pick a year for Walmart, say 2016. Find total revenue from sales, which is most of Walmart’s revenue, probably 90+ percent of total revenue. Find out the total amount paid by Walmart to their hourly employees for 2016. Then DOUBLE that figure. Walmart would have to raise revenue to cover that increase. So how much? OK, take that increase in total hourly wage cost increase and divide by current revenue. It comes out to about 2%.