Cartoon showing confusion of cause and effect

It’s easy to see a “cause and effect” relationship where there isn’t one. Or overlook one that should be as plain as daylight.

Sometimes, these errors are dramatic. And when scientists make them, a lot of people can follow down the garden path without ever looking too closely at how they got there. That’s what happened with the Hawthorne “effect.”

In November 1924, the first of a series of experiments began at Western Electric’s factory in Cicero, just outside of Chicago. Western Electric was the child of the Bell telephone company and parent to AT&T.

Photo of Hawthorne Works 1920

Aerial photo of the Hawthorne Works around 1920, Western Electric, via Wikimedia Commons

The factory complex was called the Hawthorne Works, and it was like a small city. It had a hospital, ballpark, library and much more. By the end of the decade, there would be 40,000 workers.

The electric industry wanted people to use more lighting. They sponsored the National Research Council to work with Massachusetts Institute of Technology (MIT) on experiments to show that illumination increased productivity in factory workers.

Western Electric telephone 1931

Photo of 1931 Western Electric telephone, by Lovellama (Creative Commons) via Wikimedia Commons

Three initial experiments were conducted between 1924 and 1927. You can see photos of women workers in the experiments in this collection. You would think from the way many people write about it now, that these were perfectly controlled experiments that proved that people’s productivity rose every time there was any change in lighting at all – up or down - and that it was because of something called “the Hawthorne effect.”

What people mean by that now can vary. Mostly it has come to mean that the “specialness” and novelty of being studied was all that was needed to motivate increased productivity. And that has been extended: from factory workers to all other workers, including surgical staff during operations; and from productivity to other aspects of people’s lives, including health outcomes.

The thing is, it never even happened at the Hawthorne Works. In fact, out of the first three experiments, one showed improved productivity, the second (the only one with any control) found no improved productivity, and in the third, productivity worsened. The sponsors ordered the destruction of all data – including everything that had been sent to MIT – and for no report to be written.

A manager at the Works and some researchers decided to do more experiments. Elton Mayo and his team were excited that they had discovered that workers were not only motivated by money, and they kept doing more studies till 1933. They published without a lot of data on the illumination studies, and the subsequent experiments were more about social aspects of motivation at work.

There was enough, though, to establish the myths of “the Hawthorne experiments.” It led to a radical change in thinking about management, giving birth to a new school of human relations in management that still shapes theory and the way many of us work.

What data was available would be hotly contested over the years. Henry Landsberger concluded in 1958 that the Hawthorne effect had originated “in the bias of the creators rather than in the facts it seeks to explain.” There had been, he said, “as comprehensive an indictment of a theoretical system as could be imagined.”

Then surviving data was unearthed and it surely should have dispelled any remaining belief in the experiments’ ability to prove any hypothesis at all. Critiques increased in complexity and range. The experiments’ weaknesses were dissected and debunked, including major data re-analyses in 1992, 2009 and 2011.

What were the influences that could have potentially affected productivity at Hawthorne – other than the researchers’ attention? There were many.

The women in the illumination studies had previously worked under very close supervision. But when they entered the study, their working conditions changed quite dramatically. The researchers were now in effect their supervisors, not the factory foremen. They could negotiate the terms of their working day and had more autonomy than previously.

The work done in the different departments being compared was different. The workers differed, too, with some being moved out because of low productivity, and more productive people getting their jobs.

Another big increase in productivity after the illumination experiments coincided with the Great Depression, when people were desperately afraid of losing their jobs. And by 1933, they did indeed lose their jobs.

That’s just the beginning of a long list of factors that could account for changes the researchers observed, many of them related to the lighting issue as well. For example, the researchers thought productivity went up immediately after they changed lights, but they always did that on Sundays. Even if they were not in an experimental room, workers were more productive on Monday, becoming less productive as the week went on.

There was no “Hawthorne effect” in the Hawthorne experiments.

Photo of vestige of Hawthorne Works

Photo of vestige of Hawthorne Works, Cicero, Chicago, by Harman via Wikimedia Commons

Many others who have looked for it have not been able to find it either. In 1984, John Adair reviewed educational studies that had controlled for a Hawthorne effect: only 7 of 40 found any evidence of one. Of 13 studies that sought to establish its existence, only 4 could find any sign of it.

If a Hawthorne effect were as important as many suggest in health studies as well, then you would expect there to be some detectable difference in outcomes for people who participate in controlled trials, for example, compared with those who do not. But there doesn’t seem to be.

Of course research and researchers can sometimes influence the outcomes of what they study, simply by studying. It’s just far from true that validity is always threatened by it. Yet the Hawthorne “effect” is used to trivialize results and dispute their internal and external validity. It fills a need so great, and is so deeply embedded, that it has proven “impossible to eradicate." It is a product of the imagination, but some treat it as real and many seem unaware of its dubious origins.

The durability of this old scientists’ tale tells us more about the phenomena that lead people to believe it, than it does about the influence of experimentation in people’s lives. Science is self-correcting, in theory and aspiration at least, if not as much in practice as we need it to be. In the case of the Hawthorne hypothesis, that self-correction is a mighty long time coming.


This post’s title quotes a phrase used by Jeff Sonnenfeld in his 1985 article, Shedding light on the Hawthorne studies.

The cartoon is by the author, under a Creative Commons, non-commercial, share-alike license.


The thoughts Hilda Bastian expresses here are personal, and do not necessarily reflect the views of the National Institutes of Health or the U.S. Department of Health and Human Services.