Measurement of self reported active exposure to cigarette smoke.

Abstract

Study objective--The number of cigarettes smoked per day is an imprecise indicator of exposure to cigarette smoke, and biochemical assessment of exposure is not always feasible. The aim of this study was to develop more accurate measures of self reported active exposure to cigarette smoke.

Design--Mail survey in 386 smokers, retest at one month in 94 participants (24%), analysis of saliva continine in 98 participants (25%), collection of empty cigarette packs in 214 participants (55%), collection of cigarette butts in 107 participants (28%). Ten questions and items intended to assess active exposure to cigarette smoke were tested and compared with saliva continine, the Fagerstrom test for nicotine dependence, and self rated dependence.

Setting--A population sample in Geneva, Switzerland, in 1999.

Participants--323 daily smokers and 63 occasional smokers.

Main results-Measures that were associated with saliva cotinine included the number of cigarettes smoked per day ([r.sup.2].0.36), smoking intensity ([r.sup.2]=0.40), the type of cigarettes smoked (regular versus light) ([r.sup.2]=0.04), smoking when ill ([r.sup.2]=0.15) and a single item rating of the total quantity of smoke inhaled ([r.sup.2]=0.27). A multivariate model combining the first four items explained the largest proportion of the variance in cotinine ([r.sup.2]=0.63), substantially more than was explained by the number of cigarettes per day alone, by 75% in all smokers and by 110% in daily smokers.

Conclusions-The study identified measures of exposure to smoke that reflect saliva cotinine better than the number of cigarettes per day. These measures can be used in studies of the dose related risk of smoking and in smoking reduction studies. (I Epidemiol Community Health 2001;55:674-680)

An accurate measurement of self reported exposure to cigarette smoke is useful for the assessment of the dose related risk of smoking and for the evaluation of the effectiveness of smoking reduction interventions. [1 2] The number of cigarettes smoked per day is the most frequently used indicator of exposure to cigarette smoke in epidemiological studies, but it may be inaccurate. For instance, saliva cotinine levels of smokers of 20 cigarettes per day may vary more than 10-fold, [3] and in regular smokers, the number of cigarettes smoked per day explains less than half of the variance in saliva cotinine. [3 4] The remaining variance is explained by variations in smoking (depth and duration of inhalation, number of puffs per cigarette, tapering of ventilation holes, etc), [5] by imprecise self report of the number of cigarettes smoked, by imprecise measurement of saliva cotinine or by variations in the metabolism of nicotine and continue. [4 6]

Exposure to cigarette smoke can be assessed by biochemical markers (nicotine, cotinine, thiocyanates, expired carbon monoxide, anatabine or anabasine), [7] but biochemical tests have limitations. Collecting and analysing blood or saliva samples is expensive and may not be feasible in large studies. Carbon monoxide, thiocyanates, nicotine and cotinine are not specific markers of tobacco smoke (nicotine can be obtained from patches or gums), [8 9] and assays of the most specific markers (anatabine and anabasine) are expensive. [7] In addition, many smokers may refuse to provide a sample of blood or saliva, which may create bias in biochemically validated data. [10 11] Little is known about the reliability of self reported information on other indicators of exposure to cigarette smoke, such as the number and length of cigarette butts, or the nicotine and tar yields written on cigarette packs.

The aim of this study was to develop and test the reliability and validity of several measures of self reported active exposure to cigarette smoke, and to test whether these measures were more accurate than the number of cigarettes per day in predicting saliva cotinine.

Methods

We conducted a cross sectional study to compare self reported data on exposure to cigarette smoke with objective indicators (saliva samples for cotinine analysis, cigarette butts and empty cigarette packs).

SETTING AND PARTICIPANTS

A random sample of 2000 people aged 18-70 was drawn from the official registry of Geneva residents. Potential participants received the survey by mail in March 1999. Non-respondents received a reminder postcard and two reminder questionnaires. The cover letter and the front page of the questionnaire indicated that participation was limited to current smokers and to ex-smokers who had quit smoking in the previous two years. Nonsmokers and smokers who did not wish to participate were asked to transmit the questionnaire to someone else. Previous research has shown that this procedure does not bias associations between smoking related variables. [12] We conducted a retest of the same questionnaire one month later, in volunteers only.

STUDY VARIABLES

Self reported data

We designed a series of questions intended to measure exposure to cigarette smoke. In particular, we hypothesised that asking smokers directly about their exposure would provide a useful assessment. The questionnaire was field tested in face to face interviews with seven smokers. It included the following questions about active exposure to cigarette smoke:

1 How many cigarettes do you smoke per day, on average? (Open-ended response).

2 On average, how many puffs do you take on each cigarette? (If you don't know, please count the number of puffs on your next cigarette). (Open-ended response).

3 Indicate, on a scale between 0 and 100, the intensity of your smoking. (Open-ended response).

4 In general, how much do you inhale the smoke of your cigarettes? Response options: I inhale no smoke at all; I inhale almost no smoke; I inhale smoke but not deeply; I inhale smoke rather deeply; I inhale smoke very deeply.

5 What is the total quantity of smoke that you inhale every day? (This quantity depends on the number of cigarettes you smoke, the depth of inhalation, the number of puffs, etc). (Followed by a 0-10 scale with two anchors: 0 = I inhale no smoke at all; 10 = I smoke so much that I could not inhale more smoke, even if I tied).

6 On this picture of a cigarette, please mark the length of the butts that you leave in the …