The idea that equipping homes with electrical appliances and other "modern" household technologies would eliminate drudgery, save labor time, and increase leisure for women who were full-time home workers remained largely unchallenged until the women's movement of the 1970's spawned the groundbreaking and influential works of sociologist Joann Vanek and historian Ruth Cowan. Vanek analyzed 40 years of time use surveys conducted by home economists to argue that electrical appliances and other modern household technologies reduced the effort required to perform specific tasks, but ownership of these appliances did not correlate with less time spent on housework by full-time home workers. In fact, time spent by these workers remained remarkably constant―at about 52 to 54 hours per week―from the 1920's to the 1960's, a period of significant change in household technology. In surveying two centuries of household technology in the United States, Cowan argued that the "industrialization" of the home often resulted in more work for full-time home workers because the use of such devices as coal stoves, water pumps, and vacuum cleaners tended to reduce the workload of married-women's helpers (husbands, sons, daughters, and servants) while promoting a more rigorous standard of housework. The full-time home worker's duties also shifted to include more household management, child care, and the post-Second World War phenomenon of being "Mom's taxi."