This is an edited excerpt from Jeremy Greenwood’s new book “Evolving Households: The Imprint of Technology on Life” published in January 2019 by The MIT Press.

In the 1800s, the mother in most American households worked at home surrounded by an average of six children. In a world without running water, central heating, and electricity, housework was laborious. But then, the Second Industrial Revolution introduced electricity and labor-saving household appliances. Additionally, the value of physical strength declined as machinery took over strenuous tasks.

It’s not a stretch to say that these developments changed the division of labor in the home, liberating married women from household tasks and leading to a dramatic increase in their labor-force participation.

Economic models can shed light on this change and others, like the drop in fertility and baby boom, decline in marriage, women’s liberation, increase in premarital sex, upswing in life expectancy and health care expenditures, and movement toward longer retirement. All of these trends characterize a dramatic transformation of daily life made possible by technology.

‘Home as a small factory’

Household production didn’t become part of economic theory until the 1930s, when Margaret Reid introduced the notion in her University of Chicago Ph.D. dissertation. Household production theory treats the home as a small factory. Reid writes:

The household is our most important economic institution. Yet economics of household production is a neglected field of study. With few exceptions the interest of economists has been concentrated on that part of our economic system…organized on a price basis. The productive work of the household has been overlooked, even though more workers are engaged in it than any other single industry.

Reid reported that housewives’ services generated $15.3 billion in 1918—25 percent of a national $61 billion income. Even still, not until 1965 did economist Gary Becker used modern microeconomic theory to formalize the notion of household production.

In 1900, just 5 percent of married women worked; by 2000, this had risen to 61 percent. What can explain this jump? As female labor supply rose, time spent on housework declined. In 1900, the average household spent 58 hours a week on housework, including meal preparation, laundry, and cleaning—a figure that dropped to 18 hours in 1975. At the same time, the number of paid domestic workers declined, presumably due, in part, to the labor-saving nature of household appliances. Hence, the time spent on the more onerous household chores declined considerably.

Other factors also changed, including a four-fold rise in general wage levels. Real wages rose due to technological progress in the market sector that increased the marginal product of labor. That is, for any given level of employment in the market sector, an extra unit of labor could produce more over time. This made labor more valuable. And the gender wage gap also shrunk. In 1900, a working woman earned about 50 percent of what a man did, and by 2000 this number had risen to 72 percent.

The appliance boom

The beginning of the 20th century saw the start of the Second Industrial Revolution, an era connected with the introduction of electricity, the automobile, and the petrochemical industry. It also witnessed the advent of new household technologies now fixtures of everyday life: central heating, dryers, electric irons, frozen foods, refrigerators, sewing machines, washing machines, and vacuum cleaners.

To understand the impact this had on the home, try to imagine the tyranny of household chores in 1890, when only 24 percent of houses had running water and none had central heating. Each year, the average household lugged around seven tons of coal and 9,000 gallons of water.

Laundry was a major operation. Though mechanical washing machines were available as early as 1869, this invention really took off only with the development of the electric motor. In 1900, 98 percent of households still used a 12-cent scrub board to wash their clothes. Water had to be transported to the stove to be heated by burning wood or coal. Clean clothes were rinsed and wrung out by hand or using a mechanical wringer, hung to dry, then ironed using heavy flatirons heated continuously on the stove.

The actual amount of time freed by modern appliances is somewhat speculative. Controlled engineering studies documenting time saved on a specific task by use of a particular machine would be ideal. Unfortunately, these studies are hard to come by—although there was one such study in 1945-1946 of 12 farm wives comparing time spent doing laundry by hand versus using electrical equipment. The women also wore pedometers.

The researchers reported on one subject, Mrs. Verett, in detail. Without electricity, she did her laundry in the manner described above, though using a gas-powered washing machine instead of a scrub board. A 38-pound load of laundry took her about four hours to wash and another 4.5 to iron. After electrification, Mrs. Verett had an electric washer, dryer, and iron, as well as a water system with a heater; it took 41 minutes to do a similar load and 1.75 hours to iron it. The woman walked 3,181 feet to do the laundry by hand, and only 332 feet with electrical equipment. She walked 3,122 feet when ironing the old way, and 333 the new way.

At the start of the Second Industrial Revolution, women’s magazines were filled with articles extolling the virtues of these appliances, the new domestic servants. For example, in 1920, an article in the Ladies’ Home Journal entitled “Making Housekeeping Automatic” claimed that appliances could save a four-person family 18.5 hours a week in housework.

Applying scientific principles to the home

While the development of new consumer durables was important in liberating women from the shackles of housework, so too was applying the principles of scientific management to the home. Researchers began studying domestic tasks with the aim of improving their efficiency, and Christine Frederick was an early advocate.

She was captivated by the fact that a man named Frank Gilbreth had increased the output of bricklayers from 120 to 350 bricks per hour by applying the principles of scientific management. He placed an adjustable table by the bricklayer’s side to prevent stooping down to have to pick up a brick. He had the bricks delivered in the right position on the table, to avoid the workers needing to turn each one right-side up, and he taught bricklayers to pick up bricks with their left hands and simultaneously take trowelfuls of mortar with their right.

Following Gilbreth, Frederick applied the idea to dishwashing, breaking it down into three tasks: scraping and stacking; washing; and drying and putting away. She then computed the correct height for sinks. She discovered that dishwashing could be accomplished more efficiently by placing drainboards on the left, using deeper sinks, and connecting a rinsing hose to the hot water outlet. In her estimate, this saved 15 minutes per dinner.

Frederick and others in the home economics movement had a tremendous impact on appliance and house design. Take the kitchen, for example. An 1800s kitchen was characterized by a large table and isolated cupboard. An organized kitchen with continuous working surfaces and built-in cabinets began to appear in the 1930s. The kitchen became connected with the dining room and other living areas in the 1940s, ending the housewife’s isolation.

In 1924 a pair of famous sociologists studied a small town in Indiana called Middletown. They found that 87 percent of married women spent four or more hours doing housework each day. Zero percent spent less than one hour a day. The town was re-studied by sociologists at two later dates. By 1999 only 14 percent of married women spent more than 4 hours a day on housework, and 33 percent spent less than 1 hour a day. But do people actually work more today than in the past? Do women work harder than men?

Measuring the use of time

For many years now, social scientists have surveyed Americans’ use of time. In an effort to answer such questions, economists Mark Aguiar and Erik Hurst patched together various surveys to obtain a picture of what has happened to time allocations during the past five decades.

The first survey, done in 1965-1966, focused on 2,001 individuals; the final, performed in 2003, questioned 20,720 people. In 2007, Aguiar and Hurst concluded that during this time period, hours men worked in the labor market decreased by 17 percent, from 42 to 35.5 hours per week, and women’s workforce hours increased 21 percent, from about 19 to about 23 hours per week. Their worked at home decreased by more than 50 percent.

Aguiar and Hurst also found that leisure time increased for both. Precisely defining “leisure” is problematic, so they attempt to address this problem by presenting several measures. The narrowest combines time spent on “entertainment/social activities/relaxing” and “active recreation” and includes activities such as reading for enjoyment, relaxing, socializing with friends, watching television, and the like. By this measure, men enjoy more leisure than women.

When the notion of leisure expands to include “time spent sleeping, eating, and on personal care,” men and women spend about the same time. When it broadens further to include time spent on child care—since parents rank time spent with their children playing or reading as among the most enjoyable things they do—and even more broadly as simply time not spent working, women have even more leisure than men.

The average time spent working by an adult in the market declines with economic development. Thus, it appears that leisure is a luxury good. In other words, in richer countries, people spend more time on leisure.

Jeremy Greenwood is professor of economics at the University of Pennsylvania. The text above is excerpted from “Evolving Households: The Imprint of Technology on Life” (The MIT Press, 2019). ©Jeremy Greenwood. Reprinted with permission from MIT.