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The Myth of The "Average"

by Sam Ladner on June 25, 2008 · 0 comments

in Research Methods, product design, qualitative research, quantitative research

We bandy about the word “average” all the time. What exactly IS an average, and how does it help design research?

Use the average to quickly summarize something that is already a number: minutes, ages, heights, visits, etc. Don’t use the average to explain something that needs more detail. And keep in mind, the average gets “dragged up” or “dragged down” by extreme values. Sometimes it doesn’t tell you much of anything.

An example design research project might be about how people use their stoves in their kitchens. How can we use “the average” to help us design a new stove?

The average, in statistical language, is actually called “the mean,” which is a measure of “central tendency.” Researchers use central tendency to describe all their results quickly. Other measures of central tendency include the mode (the most common response) or the median (50% of responses are higher than this; 50% are lower).The mean describes the “typical” or average result.

But here’s the big myth: there is no such thing as “the average” in your data. If you ask 500 people to rate your new stove design on a scale of 1 to 10, and the average is 4, there is no guarantee that any single person actually said 4! In fact, the majority of responses could be higher than 7, but some 1s or 2s could “drag down the average.”

Worse, it makes no sense to use the “average” or “typical” in qualitative research. If you do interviews or observations, there is no way to calculate “the average.” So when you say, “the typical person has a four-element stove,” you’re actually doing a calculation. This may be actually quite false. What you may mean to say is “most people in our study have a four-element stove” (which is the mode).

Qualitative research does not accept the “typical.” It actually looks at each case individually and in enough detail to allow for exceptions or outliers. There is no “typical” case in qualitative research because you do not do calculations. You do not summarize your data in that reductionist way.

That said, how could you use “the average” in your kitchen stove study?  You can do a back-of-the-envelope calculation to summarize your data. The “average age” of your respondents, for example, will tell you about how old people are. The “average number of minutes spent cooking” will give you a snapshot of how long people spend in their kitchens. The “average purchase price of a stove” will also give you a quick snapshot. Using “the average” is to quickly summarize something that is already a number.

But the “average use of the stove”? That doesn’t make sense. Nor does the “typical grocery shopping process,” or the “average complaint of stove use.” These cannot be summarized in “the average.”

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Categories: Research Methods · product design · qualitative research · quantitative research

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