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Does modern research prescribe 40 hour workweeks, and agree that

  1. increasing hours doesn't proportionally increase productivity
  2. you turn in less and worse work, and risk dangerous mistakes
  3. longer workweeks turn counter-productive after some time
  4. it's applicable to white-collar workers and operators of industrial machinery alike

I'm most interested in the fourth item. Most who repeat the claim gloss over it.

I'm also personally curious about whether this is applicable to early-20s people with no dependents (spouses and children), who can resist fatigue better and don't look forward to loved ones after work.

Examples of the claim

A few articles claim that working more than 40 hours per week makes you less productive. Longer workweeks eventually make you less productive than 40-hour work weeks.

From "Stop Working More Than 40 Hours a Week", Inc.com

There's a century of research establishing the undeniable fact that working more than 40 hours per week actually decreases productivity.

In the early 1900s, Ford Motor ... discovered that the "sweet spot" is 40 hours a week–and that, while adding another 20 hours provides a minor increase in productivity, that increase only lasts for three to four weeks, and then turns negative. ...

People who put in a solid 40 hours a week get more done than those who regularly work 60 or more hours. ... In every case that I've personally observed, the long hours result in work that must be scrapped or redone

And it's proven from established industries for decades as in "Bring back the 40-hour work week", Salon:

Business owners discovered that when they gave into the union and cut the hours, their businesses became significantly more productive and profitable. ...

In 1937, the 40-hour week was enshrined nationwide as part of the New Deal. By that point, there were a solid five decades of industrial research that proved, beyond a doubt, that if you wanted to keep your workers bright, healthy, productive, safe and efficient over a sustained stretch of time, you kept them to no more than 40 hours a week and eight hours a day. ...

Knowledge workers actually have fewer good hours in a day than manual laborers do — on average, about six hours, as opposed to eight.

Why I'm skeptical

These articles make recommendations for the modern white-collar worker, but they use decades-old research on factory workers. In addition, some key points were not backed up by any research, but only by anecdote. Companies described in the articles are extreme examples.

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    The key here is sustained extended hours. Long days as the exception can maintain productivity especially when working toward a short term goal. The article even says as much. – Chad Dec 12 '12 at 14:15
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    Productivity is relatively easy to quantify in a manufacturing setting and very, VERY difficult to quantify for the "knowledge workers" of the modern economy. I'm not sure that much more can be said than that the general principle seems self-evident: maximum effort cannot be sustained indefinitely and that optimal long-term production arises from something that does not trigger "burn out." – Larry OBrien Dec 13 '12 at 18:15
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    Interesting related claim made by (at least) the left parties in Germany and Sweden; they propose to decrease the working week to 35 or even 30 hours, arguing that it would increase human health (and productivity) significantly. – gerrit Dec 13 '12 at 18:17
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    Personally, I don't care if I'm less productive as long as I'm making more money either way. – jdstankosky Dec 13 '12 at 19:37
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    These subjective claims are used in objective measurements of worker productivity. The Fortune 500 also uses measurements for leave of absences, illness, turn-over and worker satisfaction-I didn't explain their measurements- so I don't see why something similar couldn't be used on a national basis. This is by no means a simple thing to define. – Razie Mah Apr 16 '14 at 8:15
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The question seems to be more scientific, but also comes with a lot of personal opinions and experience, since we probably all work.

40 hours of working might be too much already.

There have been numerous studies that working more than 8 hours a day may literally kill you. So, we can rest assure that this surely won't increase your productivity in the long run. This Forbes Article has some links to actual studies in it.

This article in Pick the Brain discusses how 8 hours, and 9 to 5, does not go together with a natural productivity cycle. The author claims that:

only 3-4 hours a day could be classified as highly productive."

Even though this is his personal opinion, when you start searching for more resources about this claim they will back it up.

It is a fact that flexible working hours are becoming more popular. Where the focus does not lie on being at an office for 8 hours a day, but that you do your tasks and assignments in a given period of time. Be it in the morning in the evening. Many Studies and articles can be found on this issue:

Here is a basic chart of European countries where hours worked is compared against productivity. Note how the Dutch are low in hours, but high in productivity.

Here's a nice link to a Harvard Business School Article which in short says:

Forget multitasking and long hours. The best way to increase personal productivity is to work faster, look for parallel opportunities, and focus on the big wins.

Conclusion: 40+ will definitely NOT be more productive when they are spent non-stop in a working place. 40 hours spread out over 8 hours a day might already not be efficient. The future will be not so much working less, but more efficient, with more room for personal/family time.

EDIT: Removed double reference and got rid of some personal opinions.

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    The entire point of my edit/bounty is to see if the claims in that particular article (the Salon.com one) are actually substantiated elsewhere - this link is also present in the original question. – enderland Jan 28 '13 at 16:46
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    Reiterates the claim (" If you turn this number into 9 or 10 this number probably won't rise much significantly.") without reference and then provides vaguely related quotes that don't quite (or at all) go to the point. Nothing substantive here. – dmckee Jan 28 '13 at 17:52
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    Correlation does not mean causation. The fact that the Dutch work less hours per week may be a consequence of their high productivity, or it may be because of some other common factor (e.g. a large highly-skilled labour force may lead to productivity improvements and job-share arrangements) – Oddthinking Dec 29 '13 at 10:10
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    @Oddthinking - No, but it's at least a hint that it's worth looking closer at the underlying relationships. Correlation may not mean causation, but it's not nothing, and should not be dismissed or ignored offhand. – Desty Jan 19 '14 at 20:36
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    Note that there the figure in question has productivity as a rate (per hour worked) rather than an absolute productiviity. As I read the question, the focus is on total productivity (eg per week) rather than per hour worked. The 'optimal rate of productivity' might occur at 10 hr per week, 20 weeks per year, but this isn't practical because it results in lower total productivity. – David LeBauer Jan 15 '15 at 20:24
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First it's important to understand broadly what workforce productivity is, please see Wikipedia's page on Workforce productivity

The OECD defines it as "the ratio of a volume measure of output to a volume measure of input".1 Volume measures of output are normally gross domestic product (GDP) or gross value added (GVA), expressed at constant prices i.e. adjusted for inflation. The three most commonly used measures of input are:

hours worked;
workforce jobs; and
number of people in employment.

Commonly understood, it's very difficult to imagine that working fewer hours increases productivity. However, the education, health and satisfaction level of workers is also very important. Increases in those levels can make up for fewer hours worked to some degree. When a business would would like to implement these they offer more benefits, industry specific training programs and can make the management process more democratic in certain ways.

Also:

recent research has examined why U.S. labor productivity rose during the recent downturn of 2008–2009, when U.S. gross domestic product plummeted.

Lay-offs would be the obvious reasons, but there are other reasons for this and it will be discussed.

The changes to the 21st century work-force have made highly skilled "knowledge workers" more "productive" even while working longer hours than 40 hours per week. Factory workers are increasingly skilled workers now, too in Europe; but over-working factory workers may also cause industrial accidents, so it is not only a "productivity" issue, as you mention. Factory work is very monotonous, which makes it actually more mentally stressful, which is a major reason why their hours must be kept down to prevent bad quality work.

Worker productivity can be defined in a number of ways. Measurements try to approximate work quality and quantity. One issue that is consistently re-evaluated is whether sleep deprivation or working longer hours causes more medical mistakes (sort of like an industrial accident in principal). "A review of studies concerning effects of sleep deprivation and fatigue on residents' performance." Samkoff JS1, Jacques CH.

The data presently available suggest that sleep-deprived or fatigued house officers can compensate for sleep loss in crises or other novel situations. However, sleep-deprived residents may be more prone to errors on routine, repetitive tasks and tasks that require sustained vigilance, which form a substantial portion of residents' workload. The authors concur with the recommendation of the Executive Council of the Association of American Medical Colleges that the total working hours for residents should not exceed 80 hours per week averaged over four weeks.

A "routine paperwork error" can occasionally be a very serious error as well that might also kill someone, but according these meta analysis is doesn't occur until over 80 hours/week. A mediocre and sleep deprived doctor is however much more productive than no doctor, but a bad doctor can be less productive than no doctor, as their job is to improve your health, not make you sick, in other words. This is a very extreme case, but in general, it shows the principal that as the knowledge level goes up, the more it makes sense to promote long work hours for the profession even if it causes a decline in work quality up to a certain point. I'm setting the point at increased accidents, although Ford in the quote in the question set his at unacceptable rates of unacceptable quality products and one or other would still be most appropriate to any modern factory.

In regards to other "knowledge workers" or office workers, their productivity is as human resources- seen in terms of the annual financial position of the company minus the cost of the workers salaries and benefits. The US department of Labor tracks employment data by full time and part-time workers and tries to keep track how many hours people are working. Since the Great Recession of 2008, there has been more part-time employment and a drop in hours worked hourly. But there is much evidence that many workers, especially the full-time, working greater than 40 hours/ week has been increasing.

This is a long-term trend that has helped companies to strengthen financial positions through this process, so their workforce is more "productive" for them, as defined.

Why High Earners Work Longer Hours (National Bureau of Economic Research, 2013)

During most of the 1900s, the hours of work declined for most American men. But around 1970, the share of employed men regularly working more than 50 hours per week began to increase. In fact, the share of employed, 25-to-64-year-old men who usually work 50 or more hours per week on their main job rose from 14.7 percent in 1980 to 18.5 percent in 2001.

The linked paper examines some of the reasons for this change and theorizes that much of it has occurred because high income workers make more money in benefits if they work more hours. As suggested before, benefits, training and democratic input are encouraged in companies to increased productivity BUT also usually these accompany more hours worked too. Many more hours in many cases.

So, the statement "increasing hours doesnt proportionally increase productivity" is true for some people and not for others and the law of diminishing returns always applies in all cases. At this time in the US, the number of people who are beneficial for a company working long hours is lower than those that can work roughly 40 hour/ week and be "productive"

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    I'm having a little trouble putting together all the threads in your answer, but I think your key argument ties knowledge workers hours to "...has helped companies to strengthen financial positions." But I'm not sure that I see any hard evidence that "places where people work longer hours" are enjoying stronger financial positions (much less stronger gains compared to similar companies where shorter hours are worked). – Larry OBrien Apr 17 '14 at 3:04
  • @LarryOBrien Not at all. The OP didn't define productivity at all, so its problematic to both prove a definition and prove why it matters in a page. The sources linked are mostly people saying something to the effect that if you feel better you are more productive, but that's not the scientific measurement of this. I will see if I can back up the claim as you are ask. – Razie Mah Apr 17 '14 at 4:28
  • @LarryOBrien What am I saying? Yes. But, as far as stronger evidence it can't be provided. Different companies occupy different positions in the market, so company X hires the top 100's average students but pays them far less and they work an average of 40 hours/week. It may still make more net profit than company Y a Fortune 500 company in any given year. The point of this answer is mostly to explain that some people work more or less than 40/week and that is their "productive" hours per week. It is both unique to the person and company. – Razie Mah Apr 17 '14 at 5:24
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    "it's very difficult to imagine that working fewer hours increases productivity" - I thought that would be very easy to imagine. Do too many hours a week, and you come to work tired and entirely unmotivated and do nothing useful in 60 hours instead of doing plenty of good work in 40 hours. – gnasher729 Jul 28 '14 at 9:57

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