Some tests of a four-day workweek suggest output can be maintained, compared to a five-day workweek, at least in a test. Some skeptics might wonder whether the stable output, 20 percent less work time pattern can be maintained in a permanent, post-test environment, as studies in the past have shown that output improves when people are in a test situation.
That Hawthorne effect refers to a behavioral observation that people change (usually improve) their performance or behavior simply because they know they are being observed, studied, or given special attention, and not because of the actual intervention being tested.
For example, medical personnel hand washing increased 55 percent when personnel were in a test of hand washing.
The point is that we cannot generalize from the results of limited-time tests because there is a significant possibility that output or behavior actually improves simply because people know they are being watched and evaluated.
The principle was first discovered in the Hawthorne Works experiments (1924–1932) at a Western Electric factory in Cicero, Illinois. Researchers tested variables such as lighting levels, rest breaks, shorter days, and work structure changes on relay-assembly workers.
Productivity rose in almost every condition (even when lighting was dimmed), and it often fell back to baseline once the study ended.
Analysts later concluded the gains stemmed from the workers feeling noticed by researchers and supervisors, forming a cohesive “special” group, receiving sympathetic oversight, and the sheer novelty of being part of an experiment.
And that is the issue: it is not clear that a permanent four-day workweek would permanently sustain the “same productivity or output” as a five-day week, as we know that awareness of scrutiny can temporarily boost output, temporarily.
We might also argue that employee well being is enhanced, but that productivity might not be similarly improved. It is hard to evaluate the productivity implications of “burnout,” for example. Many of us might note casually that many workers do not seem to produce as efficiently on Friday as at the beginning of the workweek, for example.
In other words, the marginal output on day five might be low enough that a shorter workweek might possibly not damage overall productivity very much.
There also is the Pygmalion Effect (also called the Rosenthal effect or teacher expectancy effect), a psychological phenomenon where higher expectations from one person (a leader, teacher, or supervisor) lead to improved performance in another through a self-fulfilling prophecy.
It operates via subtle behavioral changes: when expectations are raised, the "expecter" provides more support, opportunities, feedback, encouragement, and trust; the "expectee" internalizes this, boosts self-efficacy and motivation, expends greater effort, and ultimately performs better, often confirming the original high expectations.
The Hawthorne Effect is a legitimate reason to view short-term pilot results with healthy skepticism. On the other hand, accumulating evidence from longer follow-ups, real-world scaling (Iceland), and high continuation rates indicates that genuine efficiency gains, reduced fatigue, and better focus from the shorter schedule are also at work.
One might argue that if output over a four-day week remains at least the same as was seen with a five-day week, then the prior level was substantially suboptimal and inefficient, involving waste, fatigue-driven drag, and diminishing (or even negative) marginal returns on the fifth day or later hours.
The law of diminishing marginal returns applies to labor hours just as to other inputs. Adding hours beyond 35 to 48 per week (context-dependent) yields progressively less additional output per hour, as fatigue, errors, and disengagement rise.
The point is that longer working hours might lead to output-per-hour falling as total hours climb.
In trials, workers might have achieved the same (or more) total output in 20 percent less time by becoming more focused and rested. Also, less procrastination, fewer unnecessary meetings, and less "performative" busyness might also have occurred.
In that view, the fifth day wasn't "producing" proportionally; it was often recovery from the first four. Hidden costs (burnout, sick days, turnover) made the five-day model less efficient societally. In other words, we weren't as productive as we thought, we were just working more.
Long-term, recovered workers sustain higher innovation and lower error rates.
Of course, in some cases there is an opportunity cost. In theory, that fifth day could fund deep work, skill-building, research or development collaboration, or innovation sprints that compound future output far beyond maintenance.
A hyper-optimized culture might squeeze even higher total production by treating every hour as investment rather than default leisure.
Much could hinge on the type of firm; the outputs; employee commitment and other inputs. Dysfunctional firms are unlikely to suddenly be transformed into high-performance firms simply by reducing hours.
It might be the case that ‘working smarter” outperforms grinding longer, at least for firms that are well run; have high worker buy-in; good management; are highly dependent on creativity and have other hallmarks of high-performing organizations.
There are likely meaningful differences in how a four-day workweek affects different types of firms.
Creativity or insight-dependent organizations such as R&D labs, research institutes, artistic/creative agencies, design firms, innovative tech/product development might benefit more directly.
Firms whose output is standardized or routinized, such as customer service contact centers, routine manufacturing or assembly, standardized professional services like basic admin or call handling, retail operations, or shift-based public services like certain nursing or police functions might be more likely to see lower output, as they are a function of “hours available.”
The point is, there might not be one universal answer to the question “can we reduce workweeks from five to four and still maintain present output.”
