This widely-promoted trial claimed to show a 4 and 5-day work week are equally productive. It didn’t.

Robert Wiblin
7 min readFeb 26, 2019

As usual, the media failed miserably at reporting on a social science study.


In 2018 a New Zealand financial advising firm trialled switching from a 5 to 4 day work week, over a two month period.

A media push around the 19th of February 2019 promoted the idea that the trial had found workers accomplished as much work in 4 days as they previously did when working 5 days.

In particular it was a hit on Hacker News and The Guardian. But it was also covered in Fast Company, Fast Company again, ABC, NewsTalk ZB, WTSP, Fortune Magazine, MyBroadband, Women’s Agenda, LifeHacker and presumably others.

The media lapped up this idea. But the evidence for it in this trial is weak.

The news articles link to a ‘white paper’, but this report and most of the trial’s website say little about what evidence they have about reduced working hours and productivity. Instead it’s an advocacy guide to changing your company from a 5 to 4-day work week, and a plug for the firm that ran the trial.

To find that evidence you’d have to dig through to pages 8 and 9 of Prof Jarrod Haar’s research report. There are screenshots of those pages below so you can read and decide for yourself.

(Note that that and another qualitative report by Dr Helen Delaney also claim that working 4 days a week for the same pay made staff happier and more enthusiastic about their jobs in various ways. That seemed sufficiently plausible that I didn’t bother to check how good the evidence for it is.)

While ideally output would have been measured objectively — widgets produced or something — in this case it is based on a survey of 28 to 34 supervisors, who were asked about their team’s job performance before and during the trial. We are told: “Job performance was examined using a very standard construct: in-role performance, which basically reflects the way the supervisor see’s their employee team/s doing their job.”

While the report doesn’t say how in-role performance was measured, I emailed Prof Jaar and found out that supervisors were asked to score their teams on a scale of 1 to 6 on these three questions:

Robert Wiblin

I research the world’s most pressing problems and how to solve them at More about me: