“The Cat Came Back” is a gritty folk song about Mr. Johnson’s unwanted old yellow cat, who just kept coming back no matter what. As economic researchers, we have been tracking down a cat — an old economic research finding too good to be true that, just like Mr. Johnson’s cat, “wouldn’t stay away.”

The research finding, by two Princeton economists, seemed to promise that the minimum wage could be raised while increasing the employment of low-wage workers.