Different democracy measures disagree most in the gray zone between regimes.

Evidence

Cumulatively, all of these analyses suggest that in spite of high levels of correlation between various democracy data sets, there is very low or at best mediocre correlation between them in the gray zone. This suggests that any analysis focusing on the gray zone is likely to depend a lot on the particular measure used. — Gary Goertz, Social Science Concepts and Measurement, 1112

Categorization

• SEED: Essay angle: the measurement artifacts hiding inside quantitative democracy research — why ‘how democratic is Turkey?’ depends entirely on whose index you pick.
• XREF: Connects to cross-source notes on measurement validity and the constructed nature of crime statistics — proxies diverge exactly where the concept gets interesting.