The discovery sample utilized FTND data from questionnaires answered by participants in deCODE's study of ND.2, 3 Responses to FTND questions generate a score of 0–10, with higher scores representing greater ND.20 Information on smoking quantity (SQ) was also utilized, but SQ was available from a standardized smoking questionnaire used in deCODE's studies that asks: ‘How many cigarettes per day do/did you smoke on average (on most days)?' This means that current smokers answer their current consumption and former smokers refer to their consumption in the past. In cases where multiple records were available we recorded the maximum. The SQ was categorized into four levels, (1–10, 11–20, 21–30 and 31+ CPD). A total of 40 573 subjects (34 200 chip-typed) were included in the R336C analysis. Ever smokers were recruited in the years 1997–2014 as part of various Icelandic studies, and the FTND questionnaires were administered to participants in the study of ND (2004–2014). Analysis of subjects with complete FTND data showed that of those reporting 1–10 CPD, 85% had a total score of 3 or less on the FTND,
