Are there studies about the impact on per-hour output (productivity) of increasing the number of hours worked each week by employees? If every employee works 3hrs/week longer (from 41 to 44hrs), does productivity increase or decrease?
Edit About who and how much; if every worker works 3hrs more. So there is more time spent on building machines with the same amount of money. But my hypothesis is, that the more time demotivation overcompensates this marginal plus.
The closest study I could find was that by John Pencavel titled 'The Productivity of Working Hours.'
Abstract:
Observations on munition workers, most of them women, are organized to examine the relationship between their output and their working hours. The relationship is nonlinear: below an hours threshold, output is proportional to hours; above a threshold, output rises at a decreasing rate as hours increase. Implications of these results for the estimation of labor supply functions are taken up. The findings also link up with current research on the effects of long working hours on accidents and injuries.
The list of references is long. Below some citations from this 2017 article:
Studies estimating production functions based on industry-level data find mixed evidence for the returns to working hours. Whereas some studies find increasing returns to hours (Feldstein, 1967; Craine, 1973; Leslie, 1984), which could be the result of not taking capacity utilisation rates into account (e.g. Tatom, 1980), or be due to aggregation bias (e.g. DeBeaumont and Singell, 1999), other studies conclude that output is roughly proportional to hours worked per worker (Hart and McGregor, 1988; Anxo and Bigsten, 1989; Ilmakunnas, 1994). The majority of studies, however, find evidence of decreasing returns to hours (e.g. Leslie and Wise, 1980; Tatom, 1980; DeBeaumont and Singell, 1999; Shepard and Clifton, 2000).
A few studies use panels of firms to estimate the link between working time and firm or establishment productivity (Crepon et al., 2004; Schank, 2005; Kramarz et al., 2008; Gianella and Lagarde, 2011). They tend to find that output is roughly proportional to the number of hours worked.
Studies using data about individual workers in a firm, or about workers in comparable firms date back to the early 20th century [...] (Goldmark, 1912; Vernon, 1921; Kossoris, 1947). More recently, [...] Crocker and Horst (1981) find that output is proportional to hours worked, Brachet et al. (2012), Pencavel (2015), and Dolton et al. (2016) find evidence of decreasing returns to hours. A contrasting result is found by Lu and Lu (2016).
That same article is the latest paper available on the topic, which also finds a negative effect of working hours on productivity, this time for call-centre workers.
There is also this quote from a New Economics Foundation report:
In Gothenburg, Sweden’s second largest city, workers at the Svartedalens retirement home and the Toyota car factory have been working a 30-hour week. Nurses at the care home who worked six-hour days were happier than a comparable group on standard hours, and had more energy at work and in their spare time. They took half as much sick leave and were able to spend much more time undertaking activities with residents. At the Toyota factory, where a 30-hour week was introduced a decade ago, staff now produce in 30 hours 114% of what they used to produce in 40 hours. These results are encouraging other employers, in Sweden and elsewhere, to reduce working hours.
Unfortunately, they do not provide the references.
This question, as is, does not particularly describe a well-defined hypothetical.
Am I paying people a higher rate for more hours? The change in productivity might be a net positive or negative if wages rise, depending on the time allocation of the worker. Where is the change in working hours happening? If I go from 1 minute of work to 1 hour of work, productivity would presumably increase because of the time it takes to get into a state of mind to work.
These kinds of things that are needed to answer your question is related to the time allocation of labor, leisure, and household work as posited by Gary Becker in 1965. It has been revisited again by Gronau, 1977 and so on. If I am increasing working hours, I have to decrease activity in household production and leisure, so in order to say whether productivity increases if working hours increase, you have to answer what causes the marginal value of work to increase so that people willingly take on more work and less leisure.
If something like a technological advancement makes it easier for me to work, I may become more productive, but willingly take on less hours to do my work if I am on a salary/commission. This does mean the inverse, that more hours would make me less productive per se, would be true. If I am on a hourly rate, technology that makes it easier to work changes my marginal cost of effort, which changes the opportunity cost of leisure or household work. So maybe I'll take on more work in this case and become more productive.
The question isn't whether higher working hours decreases productivity. The question is why workers change working hours, and whether those voluntary changes overlap with productivity changes. The "effect" of extra hours on productivity, is ambiguous.
It might be interesting for you to compare different countries. French and German workers for example have worked less and less hours per year in the last decades whereas in the UK and US it has remained relatively stable. Only in UK has productivity not increased substantially from 2000-2015. For many years US labor productivity was below that of France and Germany. This has changed since 2000 (I presume the global crises played a major role but I am not an expert). Cf. Thomas Piketty, 9 January 2017, "Of productivity in France and in Germany"
