Other studies on the effect of local minimum wage increases in places like San Francisco and Los Angeles have found similar results, according to a recent overview published by the Center for Economic and Policy Research in Washington.

These clear benefits might help explain why Gap, the apparel chain, said last week that it would raise the minimum pay of its hourly employees to $9 an hour in 2014 and to $10 next year, which will benefit 65,000 of its 90,000 workers. The company’s chairman and chief executive, Glenn Murphy, said the move would “directly support our business, and is one that we expect to deliver a return many times over.”

Some retailers pay their workers even more. Costco, one of the most successful retailers in the country, has a starting wage of $11.50 per hour for most entry-level jobs, and its average wage for hourly workers is $21 an hour. Patrick Callans, a senior vice president for the company, said that Costco’s higher pay and benefits “allows us to attract and retain great employees.” A 2006 management case study argues that the higher pay has also helped the company keep “shrinkage,” or theft, fraud and errors, low by industry standards. For national chains, paying more than the current $7.25 federal minimum is not such a shock. Twenty-one states and the District of Columbia already have minimum wages higher than the federal level.

There is another way in which a higher minimum wage helps businesses: by increasing consumer spending. When poor families earn more, they spend more. A group of more than 600 economists, including seven Nobel laureates, recently told President Obama and congressional leaders that an increase in the minimum wage would stimulate today’s weak economy. Even Walmart, the country’s largest retailer, has previously called on policy makers to increase the federal minimum wage. A spokesman for the company recently told Bloomberg News that it was “looking at” supporting the current Democratic proposal.