Just about everything, writes Charles Arthur in the Guardian. It's a must read.
FORTUNE — These two charts at right, taken from a YouGov survey and chosen for demonstration purposes by Charles Arthur in the Guardian last week, illustrate nicely what’s wrong with statements like this (from TheNextWeb): “Android represents somewhere in the region of 80% of the smartphone market.”
That’s “simply wrong,” Arthur writes.
The purpose of Arthur’s Guardian piece was to explain — once and for all — the difference between market share and installed base, between units shipped and units sold, between new sales and replacement sales, between saturated markets and those that still have a long way to grow.
Daring Fireball‘s John Gruber calls Arthur’s story “the best piece I’ve ever seen on the folly of putting too much stock into ‘market share’ as a metric.”
As someone who spends more time than I probably should obsessing about Apple’s AAPL market share numbers, I second that.