A summary earns its place when the decision it supports remains faithful to the work underneath it. I have approved an average that gave two unequal populations equal weight. That error taught me to ask whose experience a number represents, what it leaves out and whether the person using it is being asked to decide something the evidence never measured.
I signed off the seventy per cent figure because the two regional percentages looked comparable. One region had ninety complete order-review records out of one hundred; the other had four hundred and fifty out of nine hundred. Averaging ninety and fifty gave seventy. Combining the underlying records gave five hundred and forty out of one thousand, or fifty-four per cent. The arithmetic in each region was sound. The way I allowed the regions to stand for the whole was not.
Malini Zhevqemi
Chief Data Officer