At a Labor Day rally, Kamala Harris raised eyebrows by slipping into an odd accent to inform the audience that “you better thank a union member for the five-day workweek” and many other great things. Rather than cringe at her accent, however, it’s probably better to question the accuracy of the union talking points that Harris parroted.

In the middle of the 1800s, the workweek was long—almost 70 hours in 1830. This fell in fits and starts over the next century, reaching 48 hours or so by 1929 (just before the Depression began) and slid down to 40 hours a few years later.

This decline occurred when union membership was low and occurred in virtually every industry and occupation—not just the handful that had a strong union presence. So, the time is simply wrong. The workweek fell before the New Deal gave unions power in the late 1930s. And the workweek has stayed around 40 hours ever since despite the waxing and waning of union power.

I wrote my doctoral dissertation on the shortening of the American workweek. Still, I’m not the only one who has noticed this. I surveyed economic historians and asked whether they agreed with the proposition that “the reduction in the length of the workweek in American manufacturing before the Great Depression was primarily due to the efforts of labor unions.”

Only 5 percent agreed, and an additional 25 percent agreed but with conditions, while the vast majority—over 70 percent—disagreed. Another question asked whether the reduction in the workweek was “primarily due to economic growth and the increased wages it brought.” The profession answered with a resounding “yes,” with less than 20 percent disagreeing.

The workweek fell rapidly during the decade of 1909 to 1919. I investigated this period carefully, looking at the city- and industry level to see the driving forces behind the drop in the workweek. Again, I found the expansion of the economy was the key.

When the workweek was long, workers effectively used their increased purchasing power to “buy” more time off. Now that the workweek isn’t as long, this is no longer a priority.

A wave of strikes and increased unionization during this period explained a tiny share—less than 10 percent of the drop. Surprisingly, the electrification of the economy seems to have played a more significant role—explaining about 30 percent of the workweek reduction when looking at the industry level. Before electrification, manufacturing plants relied on steam engines to power their plants, and they could get a bigger return on their investment by using the machinery for longer hours. However, electrification meant that the power company owned this expensive equipment, and factories were OK catering to their workers’ desires for a shorter workweek.

Perhaps the bumper sticker—and the politician—should give the power industry a pat on the back for giving us a more manageable workweek!