Two weeks of organic sessions, a Black Friday in the middle, and the report says: «385 sessions a day, on average». Except that no normal day came anywhere near it: the typical day had 233.
It is not a calculation error (the mean is right), it is the wrong measure for those data. Choosing the number that sums up a distribution is the first move of any analysis, and also the first way to be fooled.
Measures of position (or measures of central tendency) are there for exactly this: telling us, with a single value, where the data concentrate. Let’s look at the various means, the median, the mode, quartiles and percentiles, when to use which, and how to compute them in R in a moment.
Continue reading “Mean, median or mode? Which measure of position to use (and when to get it wrong)”