The Field Representative's Manual noted that non-filter cigarettes smoked with a separate filter should be counted as filtered cigarettes. It also noted that when a person smoked both types, interviewers should indicate the type the person usually smoked or preferred.

In the 1970 survey, a respondent representing the family (a proxy) could answer the question associated with CIGFILTER for all other family members over age 17. As self-report is typically more accurate than proxy report, researchers may want to indicate this caveat when analyzing the data or interpreting results.