Showing your work!

This think-piece by the Pew Poll is a wonderful example of transparency. They tell in detail how they categorize people.

The article goes through the history of polling and describes how each broad category (religion, income, etc) developed. This helps readers to determine when a definition changed and why. Most definitions changed when polling revealed a new category, or when a previously tiny category suddenly became meaningful, like the Nothing In Particular denomination. Sometimes the definition changed because the Census changed its categories, and Pew uses the Census as a baseline for comparison where relevant.

Must reading for metrology fans!