Adult Lifelines participants were asked whether they (had) smoked any tobacco.
Using the raw self-reported data from 1A questionnaire 1, researchers from the UMCG Department of Epidemiology calculated various derivative variables for smoking behavior (sections: lifestyle & environment and secondary & linked variables).
These derivative variables can be requested from Lifelines (data@lifelines.nl) or requested in the Lifelines catalogue.
Please note: An updated version of the smoking derivatives is available which includes derivatives for more time points and an updated version for the baseline derivaties (see updated smoking derivatives).

The following derivative variables were calculated for ~152,300 adult participants at baseline:

• Pack years
• Pack years w/o cigars
• Duration of smoking (in years)
• Recent quitter
• Recent starter
• Smoking habits
• Age at start of smoking
• Age at end of smoking
• Current smoker
• Ever smoker
• Ex-smoker
• Current number of cigarettes/day
• Current number of cigarillos/day
• Current number of cigars/day
• Current grams of pipe tobacco/day

Before the calculation of the derivative variables, the researchers checked the questionnaire smoking variables on missing and inconsistent answers. Missing and inconsistent answers were checked and corrected by comparing the original questionnaire with the answer in the database. Additionally, inconsistent answers were corrected using the validation rules listed below. The remaining items and inconsistencies were corrected according to the general principle that participants tend to underestimate their smoking habits and if a choice had to be made between two answers, the answer indicating the largest smoking history was chosen.

To enable calculation of the derivative variables, three additional variables were added:

• pyok: This variable indicates if the data given in SMK7A1-7E4 are complete (complete period from starting age (SMK2) until stopping age (SMK5) or current age (if SMK3=1 is given and number of cigarettes etc. is never missing). In this case packyears can be calculated (0=no, 1=yes).
• smokduurok: This variable indicates if the ages givein in SMK7A1-7E4 are complete and do not overlap and thus the duration of smoking can be calculated by simple summing up the durations given in item 7 (0=no, 1=yes). Overlap in ages occurs if a participant smoked 2 or more kinds of tobacco products (e.g. 10 cigarettes/day and 1 cigar/day) during the same period. Packyears can be calculated but smoking duration calculation cannot be performed by simply summing up the durations. In the present data release the smoking duration is not calculated in these cases.
• netgestopt: This variable indicates if the participant has recently quit smoking. This is the case if SMK3 is 'YES', SMK4A-D are zero or missing, SMK5 is 'YES' and SMK6 is equal to the current age (1=yes).

Derivative variables

• Dijkstra, A.E., de Jong, K., Boezen, H.M., Kromhout, H., Vermeulen, R., Groen, H.J., Postma, D.S. and Vonk, J.M., 2014. Risk factors for chronic mucus hypersecretion in individuals with and without COPD: influence of smoking and job exposure on CMH. Occup Environ Med, 71(5), pp.346-352.
• Vonk, J.M., Scholtens, S., Postma, D.S., Moffatt, M.F., Jarvis, D., Ramasamy, A., Wjst, M., Omenaas, E.R., Bouzigon, E., Demenais, F. and Nadif, R., 2017. Adult onset asthma and interaction between genes and active tobacco smoking: the GABRIEL consortium. PLoS One, 12(3).
• de Vries, M., van der Plaat, D.A., Vonk, J.M. and Boezen, H.M., 2018. No association between DNA methylation and COPD in never and current smokers. BMJ open respiratory research, 5(1), p.e000282.
• de Vries, M., Nedeljkovic, I., van der Plaat, D.A., Zhernakova, A., Lahousse, L., Brusselle, G.G., Amin, N., van Duijn, C.M., Vonk, J.M., Boezen, H.M. and BIOS Consortium, 2019. DNA methylation is associated with lung function in never smokers. Respiratory Research, 20(1), p.268.