Turning a continuous measure into a concept requires setting a threshold.

Evidence

Because these concepts like consumption, education, GDP per capita do not distinguish between the poles, I call them bipolar concepts or indicators. What makes it incomplete is that they do not conceptualize one pole or the other. To make consumption work with the concept of poverty one needs to include other criteria. In the poverty literature this is the concept of a poverty line. The concept of a poverty line completes consumption by focusing in particular on low levels of consumption. — Gary Goertz, Social Science Concepts and Measurement, 631

Categorization

• DEFINE: Defines ‘bipolar concept’ and ‘incomplete concept’ by way of the poverty line example.
• SHARE: The technical point that ‘the poverty line is a completion operation on a consumption measure’ is exactly the kind of methodological aside a single quant-minded friend would enjoy.