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====== Updated smoking derivatives ======

Adult [[start|Lifelines]] participants were asked whether they (had) smoked any [[smoking & tobacco use|tobacco]]. Using the self-reported data from [[1A]], [[1B]], [[1C]], [[2A]], [[2B]], and [[3A]], researchers from the [[https://www.rug.nl/research/epidemiology/vonk|UMCG Department of Epidemiology]] calculated various derivative variables for smoking behavior ([[sections]]: [[lifestyle & environment]] ([[Smoking & tobacco use]]) and [[secondary & linked variables]]).\\
These derivative variables can be requested from Lifelines (data@lifelines.nl) or requested in the Lifelines catalogue.\\
**Please note:** these are updated variables from the previously released [[Smoking derivatives]] from the baseline assessment.
The data on [[smoking_tobacco_use|smoking habits]] are collected in Lifelines questionnaires from multiple time-points. As a result, these data may contain inconsistencies and/or missing data. 
In October 2019, the baseline questionnaire has been validated resulting in the first version of the [[smoking derivatives]]. The updated smoking derivates incorporate the follow-up questionnaires, resulting in changes in the validated baseline data.\\
\\
===== Calculation of derivative variables =====
=== 1. Preparation ===
As a preparation step all smoking variables from the different timepoints are combined into one file.
Additionally, duplicates are removed and variables are checked on correctness.

=== 2. Calculating derivatives ===
After the overall data file has been generated, the derivative variables are calculated. This is done in an extensive syntax which can be found on the Lifelines workspace and cluster environment to read all details. In short:
  * **Smoking duration** is calculated by combining the total years a participant smoked, taking start and stop ages into account
  * **Pack years** is calculated by combining the smoking duration and the amount smoked per day (of the different smoking options). Where one pack year equals 20 cigarettes per day

=== 3. Manual validation ===
Most of the additional validations was done manually by inspecting the full longitudinal dataset of each subject separately. Because of this it is far too complicated to write all of them down. However, the general principles were as follows:
  - If the full smoking history at timepoint [[1A]] was completed, the start and stop age at later time-points will be adjusted to those given at timepoint [[1A]].
  - If the full smoking history at timepoint [[1A]] was __not__ completed, the lowest start and highest stop age given at all timepoints will be taken.
  - If a participant did not fill in the amount of smoking and (s)he was a non-smoker at all other timepoints, this participant will be recoded to a non-smoker for this timepoint as well.
  - If a participant did not fill in the amount of smoking and smoked before and/or after this timepoint, the amount of smoking will be calculated as the mean of before and after. (if one is missing then the other is taken)
  - If a participant reported that (s)he is a never smoker at some timepoint but at another timepoint the data shows that this is not correct, the participant will be recoded to an exsmoker with the appropriate start and stop ages.
  - If a participant reported smoking cigars at one timepoint but at all other timepoints (s)he never smoked cigars, then the number of cigars are changed to number of cigarettes.
  - If the stop age of a participant is missing, this can sometimes be calculated by taking the (rounded) age halfway between the questionnaire at which (s)he smoked and the uestionnaire at which (s)he no longer smoked.
  - Missing values for the question //"do you smoke now?"// will be estimated using possible start and stop ages at later timepoints or by taking the answer from the questionnaire before the missing one.
  - If a participant completed the questionnaires in the wrong order (e.g. 2A before 1C) the derivative variables are calculated manually

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===== Variables =====
| **Label English**                                            | **Label Dutch**                                                    | **Code**                       | **Variable**          | **Assessment**                             | **Additional information**                                                                                                                  |
| current number of cigarettes per day                         | huidig aantal sigaretten per dag                                   | cigarettes_frequency_adu_c_2   | currentcigarettes_v2  | [[1A]] [[1B]] [[1C]] [[2A]] [[2B]] [[3A]]  |                                                                                                                                             |
| current number of cigarillos per day                         | huidig aantal cigarillo's per dag                                  | cigarillos_frequency_adu_c_2   | currentcigarillos_v2  | [[1A]] [[1B]] [[1C]] [[2A]] [[2B]] [[3A]]  |                                                                                                                                             |
| current number of cigars per day                             | huidig aantal sigaren per dag                                      | cigars_frequency_adu_c_2       | currentcigars_v2      | [[1A]] [[1B]] [[1C]] [[2A]] [[2B]] [[3A]]  |                                                                                                                                             |
| current smoker                                               | huidige roker                                                      | current_smoker_adu_c_2         | currentsmoker_v2      | [[1A]] [[1B]] [[1C]] [[2A]] [[2B]] [[3A]]  |                                                                                                                                             |
| current times of use of e-cigarette per day                  | huidig aantal gebruik e-sigaret per dag                            | ecigars_frequency_adu_c_1      | currentecig_v2        | [[2B]] [[3A]]                              |                                                                                                                                             |
| ever smoker                                                  | ooit roker                                                         | ever_smoker_adu_c_2            | eversmoker_v2         | [[1A]] [[1B]] [[1C]] [[2A]] [[2B]] [[3A]]  | both current and ex smokers are regarded as ever smokers                                                                                    |
| ex smoker                                                    | ex-roker                                                           | ex_smoker_adu_c_2              | exsmoker_v2           | [[1A]] [[1B]] [[1C]] [[2A]] [[2B]] [[3A]]  |                                                                                                                                             |
| never smoker                                                 | nooit gerookt                                                      | never_smoker_adu_c_1           | neversmoker_v2        | [[1A]] [[1B]] [[1C]] [[2A]] [[2B]] [[3A]]  |                                                                                                                                             |
| packyears (cumuative smoking history)                        | pack years (cumulatieve rookgeschiedenis)                          | packyears_cumulative_adu_c_2   | py_v2                 | [[1A]] [[1B]] [[1C]] [[2A]] [[2B]] [[3A]]  | 1 packyear is 20 cigarettes per day for 1 year or 10 cigarettes for 2 years etc. ** * **                                                    |
| current grams of pipe tobacco per day                        | huidig aantal gram pijptabak per dag                               | pipetobacco_frequency_adu_c_2  | currentpipe_v2        | [[1A]] [[1B]] [[1C]] [[2A]] [[2B]] [[3A]]  |                                                                                                                                             |
| recent starter                                               | recente starter                                                    | recent_starter_adu_c_2         | recent_start_v2       | [[1A]] [[1B]] [[1C]] [[2A]] [[2B]] [[3A]]  | A person that recently started smoking, is currently still smoking, but for less than a year, is categorized as a recent starter ** * * **  |
| duration of smoking in years                                 | duur van het roken in jaren                                        | smoking_duration_adu_c_2       | smokingduration_v2    | [[1A]] [[1B]] [[1C]] [[2A]] [[2B]] [[3A]]  |                                                                                                                                             |
| age at stop smoking                                          | leeftijd bij stoppen met roken                                     | smoking_endage_adu_c_2         | smkstop_v2            | [[1A]] [[1B]] [[1C]] [[2A]] [[2B]] [[3A]]  |                                                                                                                                             |
| smoking habits                                               | rookgewoonten                                                      | smoking_habit_adu_c_2          | smoking_v2            | [[1A]] [[1B]] [[1C]] [[2A]] [[2B]] [[3A]]  | ** * * **                                                                                                                                   |
| age at start smoking                                         | leeftijd bij begin roken                                           | smoking_startage_adu_c_2       | smkstart_v2           | [[1A]] [[1B]] [[1C]] [[2A]] [[2B]] [[3A]]  |                                                                                                                                             |
| total number smoked per day (all types except e-cigarettes)  | totaal aantal gerookt per dag (alle soorten behalve e-sigaretten)  | total_frequency_adu_c_1        | totsmkday             | [[1A]] [[1B]] [[1C]] [[2A]] [[2B]] [[3A]]  |                                                                                                                                             |

* Please note that in contrast to the previous calculation, cigars are now regarded to as 1 cigarette (and not as 3)\\
** Additional information on smoking_habit_adu_c_2 with four categories: never-smoker, current smoker, ex-smoker, and recent starter. A person that smokes or has smoked for less than a year, is not seen as a smoker. Thus, a person that has smoked for a few months and then stopped is categorized as a 'never-smoker'. A person that recently started smoking and is currently still smoking is still seen as a never smoker because that person currently smokes for less then a year. However, these persons are categorized as a 'recent starter'.
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