October 23, 2012

Why is this week unlike every other week?

Researchers frequently want to find out how people behave in a typical day or week.  It turns out, though, that it’s often better to ask them what they did this week, even though this week may be far from typical.

It seems that a ‘typical’ day or week is actually a sort of Platonic ideal rather than a mean or median: in a ‘typical’ week, perhaps you exercise every day, but this particular week you missed a couple of days.  In a ‘typical’ week you eat vegetables every evening, but this particular week there was a social event at work and you didn’t.  In a typical week, you work five days, but this week there was a holiday on Monday.

The graph below shows the distribution of working hours reported for ‘usual’ weeks in two US government surveys and for “last week” in a third survey

People who work a lot tend to report more hours for a ‘usual’ week than last week. People who work less than half time tend to report fewer hours for a ‘usual’ week than last week.

The Washington Post article that provided the graph says that people who claim to work long hours are “lying”, but it’s more complicated than that.  Presumably these are people who ‘typically’ work long hours but reasonably often have to leave work ‘early’ to handle some part of the rest of their lives.  Conversely, the people at the low end of the distribution may have a regular part-time job that provides their ‘usual’ hours of work, but fairly often have over-time or additional jobs so that the average week has more work than a ‘usual’ week.   They aren’t lying, they just aren’t answering the question you thought you wanted to ask.


Thomas Lumley (@tslumley) is Professor of Biostatistics at the University of Auckland. His research interests include semiparametric models, survey sampling, statistical computing, foundations of statistics, and whatever methodological problems his medical collaborators come up with. He also blogs at Biased and Inefficient See all posts by Thomas Lumley »