Compared to what?

From Sonia Pollak’s winning Stat of the Week

Now, if we look at the number of people who lodged a claim on Christmas day: this was 3040.
In the 07/08 financial year there was 1.8 million claims, an average of around 5000 a day.

Telling people to look out over the Christmas period and take care is good, but from this, it would appear that actually, Christmas day has less, if not accidents, claims than the average day.

Another famous example in journalism is by Eric Meyer, (via Robert Niles)

My personal favorite was a habit we use to have years ago, when I was working in Milwaukee. Whenever it snowed heavily, we’d call the sheriff’s office, which was responsible for patrolling the freeways, and ask how many fender-benders had been reported that day. Inevitably, we’d have a lede that said something like, “A fierce winter storm dumped 8 inches of snow on Milwaukee, snarled rush-hour traffic and caused 28 fender-benders on county freeways” — until one day I dared to ask the sheriff’s department how many fender-benders were reported on clear, sunny days. The answer — 48 — made me wonder whether in the future we’d run stories saying, “A fierce winter snowstorm prevented 20 fender-benders on county freeways today.” There may or may not have been more accidents per mile traveled in the snow, but clearly there were fewer accidents when it snowed than when it did not.

There’s an important distinction to be made here, in partial defense of the ACC figure.  Even though more people have accidents on a typical day, it still makes sense to say that a particular accident was because of Christmas — injuries caused by Christmas trees, or carving hams, or stepping on little plastic toys that are supposed to transform into slightly different little plastic toys but now won’t.  If it hadn’t been Christmas there would have been more accidents, but different ones, and probably happening to different people.   This is only partially a defence of the ACC, because they don’t seem to have made any attempt to separate Christmas-attributable injuries from ordinary day-to-day injuries that just happened to occur during the holiday.

Sonia was comparing Christmas injuries to non-Christmas injuries, the ACC was trying to compare the typical Christmas with an improved version where people were more careful about the special hazards of the day.  “Compared to what?” is the fundamental statistical question.