Measurability is the main difference between a concept and a variable. Concepts are mental images or perceptions and therefore their meanings vary markedly from individual to individual, whereas variables are measurable, though, of course, with varying degrees of accuracy. A concept cannot be measured whereas a variable can be subjected to measurement by crude/ refined or subjective/objective units of measurement. Concepts are subjective impressions which, if measured as such would cause problems in comparing responses obtained from different respondents. According to Young:
Each collaborator must have the same understanding of the concepts if the collaborative data are to be similarly classified and the findings pooled and tested, or reproduced. Classification and comparison demand uniform and precise definitions of categories expressed in concepts. (1966: 18)
It is therefore important for the concepts to be converted into variables (either directly or through a set of indicators) as they can be subjected to measurement, even though the degree of precision with which they can be measured markedly varies from one measurement scale to another (nominal, ordinal, interval and ratio).Table 5.1 gives examples of concepts and variables to illustrate the differences between them.
Source: Kumar Ranjit (2012), Research methodology: a step-by-step guide for beginners, SAGE Publications Ltd; Third edition.