How to read a population report without fooling yourself

A population report is a census of submissions, not a census of surviving cards. Every figure it shows is downstream of who chose to submit, when they submitted, and what they expected to get back.

The most useful number is rarely the population at a grade. It is the population above that grade. A card with 800 examples at grade 9 and 12 above it behaves very differently from one with 800 at grade 9 and 600 above it.

Resubmission also distorts the picture. Cards that cross from one grader to another, or that are cracked and resubmitted, can appear twice in aggregate data. Treat short-run census movements with caution.

For collection construction we treat population data as one input among several: transaction frequency, print history, condition sensitivity of the print run, and the observable spread between grades.