|Canon||Meaning in classification||Application to questionnaires|
|Differentiation||Not too many items in one class||Don't ask questions for which almost everyone will give the same answer (for one thing, such questions make it very difficult to obtain statistically significant results)|
|Non-concomitance||Not too predictable from another characteristic||Don't ask redundant questions (except for the specific purpose of checking intra-respondent reliability)|
|Relevance||Useful for intended uses and users||Don't ask questions to which you don't really need the answer; for example, don't ask for personal details such as age unless these are important.|
|Ascertainability||Easy to assign items to classes||Don't ask questions that respondents cannot readily answer (for example, questions that require looking up some other source of information)|
|Permanence||Not too many items changing class||Don't ask questions to which the answer is likely to change quickly: this creates problems with reliability.|
* Ranganathan, S.R. 1963. Prolegomena to library classification, ed. 3. New York: Asia Publishing House. 144-153.