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7. Smoking

Smoking is a strong risk factor for cardiovascular diseases, cancer and several other chronic diseases. This report focuses on tobacco smoking, leaving out smokeless tobacco use.

7.1 Definitions

The WHO has published standardized guidelines for measurement of smoking (1). Based on these guidelines, people can be classified as smokers or non-smokers; and these two main categories can be divided into number of sub-categories.

A smoker is a person who, at the time of the survey, smokes any tobacco product either daily or occasionally. i.e. smokers can be either daily or occasional smokers. A daily smoker is a person, who smokes any tobacco product at least once a day (except that people who smoke every day, but not on days of religious fasting, are still classified as daily smokers). An occasional smoker is a person, who smokes, but not every day. Occasional smokers can be reducers, continuing occasional smokers or experimenters. A reducer is a person, who used to smoke daily but now does no longer smoke every day. A continuing occasional smoker is a person who has never smoked daily, but who has smoked 100 or more cigarettes (or the equivalent amount of tobacco) and now smokes occasionally. An experimenter is a person who has smoked fewer than 100 cigarettes (or the equivalent amount of tobacco) and now smokers occasionally.

A non-smoker is a person who, at the time of the survey, does not smoke at all. Non-smokers can be ex-smokers, never-smokers or ex-occasional smokers. An ex-smoker is a person who was formerly a daily smoker but currently does not smoke at all. A never-smoker is a person who either has never smoked at all or has never been a daily smoker and has smoked less than 100 cigarettes (or the equivalent amount of tobacco) in his/her lifetime. An ex-occasional smoker is a person who was formerly an occasional, but never a daily smoker and who has smoked 100 or more cigarettes (or the equivalent amount of tobacco) in his/her lifetime.

In addition to smokers and non-smokers we can define ever smokers. An ever smoker is a person who has smoked at least 100 cigarettes (or the equivalent amount of tobacco) in his/her lifetime. For ever smokers there is a sub-category ever daily smokers. Ever daily smoker can be a currently daily smoker, reducer or ex-smoker.

7.2 Questionnaires

In this subsection we review the smoking questionnaires used in the surveys considered in this report. We include in the review also other recent international recommendations for smoking questionnaires.

7.2.1 WHO MONICA Project

The smoking questionnaire in the WHO MONICA Project represents a compromise among different proposals and was derived from the WHO Cardiovascular Survey Methods questionnaire (2). According to the MONICA instructions, it can be self administered if it is sent to the home of the invited persons together with the invitation to the examination; or it can be administered by a technician or nurse at the screening site. The same procedure, however, should be applied throughout the study in the same centre.

Following is the WHO MONICA Project protocol for recording the smoking history (3):

SMOKING QUESTIONNAIRE (March 1992)

The MONICA Manual (3) gives the following additional instructions for the above questionnaire:

Question 1. Do you smoke cigarettes now?

Code 1 if a regular cigarette smoker. Include subjects who smoke hand-rolled cigarettes regularly.
Code 2 if a non-smoker, i.e. if a person does not smoke cigarettes at all (Go to 5)
Code 3 is used when the person smokes cigarettes but usually less than one cigarette per day (Go to 3).

Question 2. On average, how many cigarettes do you smoke a day?

Code the average number of cigarettes smoked daily. Include subjects who smoke hand-rolled cigarettes regularly (Go to 8). If the answer to Question 2 is irrelevant, i.e. the answer to Question 1 = 2 or 3, draw a horizontal line through the boxes.

Question 3. On how many days a week do you smoke cigarettes?

Code 1 if usually on one day or less a week. Include "holiday smokers" who smoke fairly regularly for a few weeks a year but only one day a week or less for most of the year.
Code 2 if usually on 2-4 days a week.
Code 3 if almost every day.

Question 4. On average, how many cigarettes do you smoke a day?

Code the average number of cigarettes smoked per day. In many cases the answer is obtained by dividing the number of cigarettes smoked per week by 7 and rounding to the nearest whole number, i.e. if the subject usually smokes 3 cigarettes at most per week, code 000; if the subject smokes on average from 4 to 10 cigarettes per week, code 001; and if 20 cigarettes at the weekend, code 003.

This should only be answered by those who have answered 3 to Question 1, otherwise skip the question.

Draw a horizontal line through the boxes if this question is skipped.

NOTE: This question is the same as Question 2 but is not asked for the same subject. If either one of the questions has been asked, the answer should be entered for Question 2 in the data transfer format.

Question 5. Did you ever smoke cigarettes regularly in the past?

Code 1 if yes.
Code 2 if No (Go to 10).

This should only be completed for Non-smokers, i.e. Question 1 = 2 and for occasional smokers Question 1 = 3.

Draw a horizontal line through the box if this question is skipped.

Question 6. When did you stop smoking cigarettes regularly?

Enter the year of smoking cessation (if the subject cannot be sure of the exact year, please give an estimate).

Question 7. If in the last 12 months

Code 1 if less than 1 month ago
Code 2 if 1-6 months ago
Code 3 if 6-12 months ago.

This should only be answered for those who replied Yes to Question 5.

Draw a horizontal line through the boxes if this question is skipped.

Question 8. What is the highest average daily number of cigarettes you have ever smoked for as long as a year?

Code the number of cigarettes smoked per day. The purpose of this question is to get a round idea of how heavily the subject has smoked in the past.

Draw a horizontal line through the boxes if this question is skipped.

Question 9. How old were you when you began to smoke cigarettes regularly?

Code age in years.

Draw a horizontal line through the boxes if this question is skipped.

Question 10. Have you ever smoked cigars or cigarillos?

Code 1 if now smoke regularly
Code 2 if No (Go to 12)
Code 3 if now smoke occasionally (less than one/day)
Code 4 if used to, but not now (Go to 12).

Question 11. How many do you smoke per week?

Enter the actual number of cigars or cigarillos smoked per week.

Draw a horizontal line through the boxes if this question is skipped.

Question 12. Have you every smoked a pipe?

Code 1 if now smoke regularly
Code 2 if No (Go to 14)
Code 3 if now smoke occasionally (less than once a day)
Code 4 if used to, but not now (Go to 14)

Question 13. About how many grams of pipe tobacco do you smoke per week?

Enter the number of grams (1 ounce = 30 grams).

Draw a horizontal line through the boxes if this question is skipped.

Question 14. For how many hours, on average each day, are you closely subjected to other people's tobacco smoke?

To be completed for occasional and non-smokers only.

"Closely subjected" in this context implies that the subject is aware of seeing and smelling, or inhaling the tobacco smoke.

Try to estimate an average for the number of hours each day over the seven days of the week, as exposure to other people's tobacco smoke may vary throughout the week.

It does not matter that the answer for many subjects will be 00 or 01, as this question aims to determine the proportion of occasional and non-smoking subjects who are exposed to other people's tobacco smoke to a substantial degree.

7.2.2 Risk factor monitoring in the Netherlands 

In the Monitoring Project on Cardiovascular Disease Risk Factors in the Netherlands the following questions were used in the period from 1987 until 1991 (4).

Subjects were classified as current, former and non-smokers.

Current cigarette smoking was estimated from the questions.
Q1: Do you smoke?
Q2: How many cigarettes do you smoke per day?

Former cigarette smoking was estimated from the following question:
Q3: Have you ever smoked cigarette regularly?
Q4. At what age did you start cigarette smoking?
Q5: How many years did you smoke cigarettes?
Q6. How many cigarettes did you smoke on average per day?

Additional questions were about smoking cigar or pipe.

In the MORGEN-project following smoking questions were used (5):

Current cigarette smoking was estimated from the questions:
Q1: Do you smoke? (If not, but did in the past -> Q2)
Q2: How many cigarettes do you smoke on average per day?

Former cigarette smoking was estimated from the follwoing questions:
Q1: Do you smoke (if not, but did in the past -> Q4)
Q4: At what age did you start cigarette smoking?
Q5: Did you ever stop smoking for a period, after which you started again?
Q6: How many cigarettes did you smoke on average per day?
Z7: At what age did you stop smoking?

Additional questions were about smoking cigar or pipe and the use of filtered of non-filtered cigarettes.

7.2.3 Risk factor monitoring in Germany

The German Federal Health Survey 1998 used questions that incorporated the ones from the WHO guidelines and in addition addressed the issues of passive smoking and quitting of smoking (6).

7.2.4 UK National Health Surveys

Question used in 1998 Health Survey for England (7):

Following coding instructions are given:

Question 2. If Question 1 = "Yes" then ask this question.

Question 3. If Question 2 = "Yes" then ask this question. If less than one a day, enter 0. If range given and can't estimate, enter mid point. If respondent smokes roll ups and cannot give number of cigarettes, code 97.

Question 5. If Question 4 = "filter-tipped cigarettes" or "plain" or "untipped cigarettes" then ask this question. Assign 2-digit code from coding card C. If not on list, code as 997.

Question 6. If Question 2 = "No" then ask this question.

Question 7. If Question 6 = "Yes" then ask this question.

Question 8. If Question 7 = "Smoked cigarettes regularly" then ask this question. If less than one a day, enter 0. If range given and can't estimate, enter mid point. If respondent smokes roll ups and cannot give number of cigarettes, code 97.

Question 9. If less than one year, code 0.

Question 10. If Question 7 = "Smoked cigarettes regularly" or "smoked them only occasionally" then ask this question. If less than one year age, code 0. If Question 10 = 0 then ask Question 10a.

Question 11. If Question 10 <> Empty and Question 10 < 2 then ask this question. If respondent has given up more than once, ask about most recent occasion.

Question 12. If Question 2 = "Yes" or Question 7 = "Smoked cigarettes regularly" then ask this question. If never smoked regularly code 97.

Question 14. If Question 13 = "Yes" then ask this question. 

Question 15. If Sex = "Male" than ask this question.

Question 16. If Age of respondent is 13 years or over then ask this question.

Additional to these questions there is a group of questions asked only from female. These questions ask about the smoking during the pregnancy. Also from all smokers the brand of the cigarettes they smoked were asked.

7.2.5 National Health and Nutrition Examination Survey (NHANES III), USA

The following smoking questionnaire was used in NHANES III during the interview at subject home (8):

Following coding instructions were given:

Question 1. If No go to question about non-smoked tobacco use (Have you ever used chewing tobacco or snuff?)

Question 2. This can be difficult to answer since it depends on the SP's interpretation of 'fairly regularly'. We want to know the SP's age when smoking became routine or became an established habit for them rather than the time when they may have first experimented with cigarettes. Record the respondent's best estimate. Enter code 000 if never smoked regularly.

Question 3. By 'now' we mean the current month or so and not necessarily whether the SP has had a cigarette today. Even the use of a very small number of cigarettes at the present time would qualify as a 'Yes' response. Enter code 1 (Yes) for respondents who indicate they have stopped smoking temporarily, for example, due to illness, but expect to begin again.

Question 4. We are interested in the current 'usual' habit, the average number smoked on a typical day. Enter a number in the first field and the appropriate code to indicate whether the answer reflects cigarettes or packs. If the SP's answer is 'it varies', probe for a more specific answer. If after probing the answer is still 'varies' enter '666'. This should only be done for those whose habit is so irregular and variable that no 'average' value can accurately reflect the SP's habit.

Question 5. Record the total duration of the amount of cigarettes specified in Question 4. We are interested in total years of smoking rather than the length of any one period of smoking.

Question 7. An approximate number is acceptable here. Enter a number in the first field and the appropriate code to indicate cigarettes per day/packs per day. Enter code 666 (varies) only after probing and only for those whose habit is so irregular and variable that no 'average' value can accurately reflect the SP's peak habit.

Question 8. The phrase 'that amount' refers to the amount smoked in Question 7. See specifications for Question 5.

Question 9. By 'one year or longer' we mean at least one year continuously off cigarettes.

Question 10. Count all of the time of cigarettes, summing up not only the long intervals of six months or more but the shorter intervals as well.

Question 11. We are looking for the point in time when the person generally quit, even if s/he had a couple of cigarettes after that point.

Question 12. See Question 4 for general guidelines. We want the person's main pattern prior to quitting. Ignore very brief aberrations in their usual habit due to their efforts to quit.

Question 13. The major distinctions important to make are whether the person had a medical problem that caused or was made worse by smoking and inspired him/her to quit, e.g. a cough, an allergy, a heart attack, ect., or whether they were influenced or motivated by other factors. If the SP quit because of an existing health problem, enter code 1 (Yes) but if s/he did not quit because of a health problem, enter code 2 (No).

Question 15. By 'now' we mean the current month or so and not necessarily whether the SP has had a cigar today. Even the use of a very small number of cigars at the present time would qualify as a code 1 (yes). Enter code 1 (yes) for respondents who indicate they have stopped smoking temporarily, for example, due to illness, but expect to begin again.

Question 16. We want the current 'usual' habit, the average number smoked on a typical day.

Question 17-19. See specifications for Questions 14-16.

7.2.6 FINBALT

FINBALT (9) is a collaborative study for monitoring health behavior and related factors in Estonia, Finland, Latvia and Lithuania.

FINBALT questions for smoking in their next surveys are:

The above questionnaire has been adopted by CINDI Programme to be used in the CINDI Health Monitor, an interview survey system in the CINDI countries (10). 

7.2.7 EUROHIS

For the needs of the WHO strategy of Health for All, the European Office of WHO has a project on international harmonization of methods and instruments for health interview surveys (EUROHIS). The EUROHIS questions for smoking are (11):

It is not known which studies have used this questionnaire or what the experience was.

7.2.8 WHO recommendation

The WHO recommendations were prepared by an international expert group and published in the WHO book 'Guidelines for controlling and monitoring the tobacco epidemic' (1). The recommended questions are:

There are following clarifications and instructions are provided for coding and for modifying the above questions, respectively:

Question 1. Those who have smoked very few (even one) cigarette(s) in their lifetime should still answer "yes" to this questions.

Question 2. Smoking 100 cigarettes is approximately the same as smoking one cigarette per day for three or four months, or occasional smoking for about one year.

Question 3. If desired, the qualification "for at least six months" could be added to preserve comparability with previous WHO definitions.

Question 4. This refers to current smoking status at the time of the survey.

Question 5. This list of items should be adapted to suit local tobacco use patterns. Some of these items may not be used and therefore should be excluded, but others not listed might be common and therefore should be included. If some items are smoked, but the average is less than one per day, use the number zero. For former daily smokers, the average should refer to the time when they were daily smokers.

Questions 6. and 7. The actual daily amount smoked should be recorded. Pre-coded categories such as 1-10 per day, 11-20 per day etc. should be avoided. This question should be asked only of ever daily smokers (i.e. those who answer "yes" to question 3 and/or who answer "daily" to question 4). Enter number of years. If less than one year, code as zero. Do not count time periods when the person was not smoking.

Question 7. This question should be asked only of ex-daily smokers (i.e. those who answer "yes" to question 3 and "occasional" or "not at all" to question 4). Enter number of years. If less than one month, code as zero. Do not count time periods when the person was not smoking. Respondents who have stopped smoking as recently as one day prior to the survey should still be classified as ex-smokers (with a duration of less than one month).

It is not known which studies have used this questionnaire or what the experience was.

7.2.9 Norwegian Age-40 Programme

The Norwegian Age-40 Programme questionnaire had questions in 15 areas of inquiry, starting with health history and ending with womens' health. Questions about smoking appeared in ninth position of this order.

7.2.10 The Italian OEC Project

The questionnaire section on smoking followed sections dealing with demographic, socio-economic, and physical activity and preceded the section on awareness and treatment of hypertension. 

7.3 Biochemical markers for exposure to tobacco smoke

Biochemical markers like thiocyanate, cotinine and expired air carbon monoxide can be used to validate smoking data collected by questionnaires. Markers can also be used to indicate smoking status or exposure to environmental tobacco smoke. 

When assessing the reported smoking status by biochemical markers one has to consider the time between filling in questionnaire and sample collection for biochemical validation. If a person fills in the questionnaire at home a few weeks before coming to the clinical examination were a blood/saliva/urine sample is collected he/she may have stopped or started smoking during that time. Also, the exposure to environmental tobacco smoke has to be assessed and taken into account when analysing the results.

Biochemical markers alone can be used as indicators for smoking status.

Exposure to the environmental tobacco smoke may depend on several factors, including the number of smokers in an enclosed area, the size and nature of the area, and the degree of ventilation. The development of new biochemical methods enables one to obtain measurements of exposure to environmental tobacco smoke by determining the uptake of specific agents in body fluids and calculating the risk relative to that of the exposure of active smokers. The uptake of individual agents from environmental tobacco smoke can be determined by biochemical measures that have been developed for assessment of active smoking behavior, as long as these measures are sensitive and specific enough for quantifying exposure to such agents by nonsmokers.

In this chapter we will briefly describe three biochemical markers: thiocyanate, cotinine and expired air carbon monoxide. Also, the use of biochemical markers in different studies will be discussed.

7.3.1 Types of biochemical markers

Thiocyanate is the chief metabolite of hydrogen cyanite, which occurs tobacco smoke, and can be used as a marker for smoking status. Thiocyanate can be measured in blood, saliva or urine (12). The major problem with thiocyanate is that it is not specific to tobacco smoking. Its advantage is longer half life than in cotinine or carbon monoxide.

The most commonly used cutoff point for blood serum/plasma thiocyanate level for current smoking is 100 µmol/l. Depending on the study, this cutoff point yields specificity of 75%-100% and sensitivity of 76%-99%. In these studies the error rate varies from 9% up to 36%. In most studies the error rate was below 30%. (13, 14)

Cotinine is the principal metabolite of nicotine and has a half-life of about 17 hours (15). It can be measured either in saliva (16), blood (17), urine (18) or hair (19). Cotinine is very specific and sensitive, but expensive to measure (20). However, in many countries the use of nicotine replacement therapy may cause problems, because it also increases cotinine.

There is no commonly agreed cutoff point for cotinine level in current smokers. In published studies the cutoff points range from 3ng/ml up to 50 ng/ml. The sensitivity of the cotinine ranges between 87%-99% and the specificity between 79%-100%. In these studies the error rate varies from 7% up to 22%. In most studies the error rate was below 20%. (12, 13, 15, 21)

Exhaled carbon monoxide (CO) measurement is cheap and gives an instant readout, but CO has a comparatively short half-life, shows diurnal variation in smokers and is confounded to some extent by environmental or occupational exposure (12).

A commonly used cutoff point for expired air CO for current smokers is 9 ppm. The sensitivity varied between 88%-100% and specificity form 84% up to 99%. The error rate in these studies was between 3%-23%. In most studies the error rate was below 20%. (12, 13)

WHO MONICA Project

In the WHO MONICA Project it was recommended that smoking questionnaire data should be validated using expired air carbon monoxide, serum cotinine or serum thiocyanate for all (100%) subjects. If the centre is not able to do validation for all subject it should do it for at least 10% of subject, irrespective of their smoking history (3). In the initial MONICA survey, thiocyanate was measured by most centres (22). However, after it was found that there was a very large variation in the distribution of thiocyanate between the non-smoking populations, the usefulness of thiocyanate was questioned (unpublished result). As a consequence, only few centres measured thiocyanate in the final survey. Serum cotinine and expired air carbon monoxide were recommended for the middle and final survey, but they were measured in very few centres only (22).

MONICA did not use biochemical markers to assess the exposure to environmental tobacco smoke.

UK National Health Survey

In the UK National Health Survey saliva cotinine was used to assess the smoking status (7).

Cigarette smoking prevalence is measured in two ways in the Health Survey for England. Informants are asked directly whether they smoke cigarettes nowadays, and cotinine levels in saliva are measured for those providing a saliva sample at the nurse interview. A saliva cotinine level of ³15 ng/ml is taken as an indication that the informant currently smokes (those who use other nicotine products are excluded). (7)

In women the cotinine based estimates of prevalence of smoking were the same as prevalence based on questionnaire, but in men cotinine estimates were 4% higher than questionnaire based estimates. This difference can be explained by cigar and pipe smoking. (7) The UK Health Survey smoking questionnaire does not ask about the current cigar or pipe smoking (see section 7.2.4).

NHANES III

In NHANES III a biochemical determination of tobacco exposure was used to assess both passive smoking and tobacco use through measurement of blood cotinine levels from specimens obtained by venipuncture in the Mobile Examination Centre from examinees aged 4 years and over. Cotinine was detected using an isotope dilution, liquid chromatography, tandem mass spectrometry method developed by the National Center for Environmental Health, CDC, which conducted the analyses. This was a newly developed method designed to detect levels as low as 0.030 nanograms per milliliter.

Other surveys

No information about biochemical markers for exposure to tobacco smoke were found for Risk factor monitoring in the Netherlands and Risk factor monitoring in Germany.

7.4 Quality assurance

7.4.1 Retrospective quality assessment report

WHO MONICA Project

The detailed description about the availability and quality of smoking questions in  MONICA is given in the Quality Assessment of Data on Smoking Behavior in the WHO MONICA Project (22).

In the final survey, 33% of the centres included in their questionnaires at least 10 out of 13 questions identical to the MONICA format. Although many centres had changed their questions for the final survey according to the MONICA model, there were still deviations between MONICA question and questions used locally. Most common deviations were:

• CIGS and EVERCIG inquire not only about cigarette smoking but also include pipe and cigar smoking in the same questions.
• CIGS and EVERCIG allow only yes/no options, so that regular and occasional smokers cannot be separated.
• EVERCIG precedes CIGS, changing the whole structure of the questionnaire.
• NUMCIGS excluded occasional smokers.
• NUMCIGS was also asked of past smokers.
• STOP inquired how many years ago the subject stopped smoking.
• STOP and IFLYEAR were combined asking the month besides the year of quitting.
• MAXCIGS excluded current smokers.
• CIGARSM, CIGAR, PIPESM and PIPE were combined, permitting only partial extraction of CIGARSM and PIPESM and preventingt distinction between current and past cigar/pipe smokers.
• DAYCIGS asked the number of smoking days per week.

7.5 Indicators used for reporting the results

The WHO recommends several prevalence figures that can be used when reporting the smoking results (1). Prevalence of smokers is the percentage of smokers among "smokers + non-smokers". Prevalence of daily smokers  is percentage of daily smokers among "daily smokers + plus occasional smokers + non-smokers". Prevalence of ex-smokers  is percentage of ex-smokers  among "ever smokers + never-smokers". Prevalence of cessation, also know as quit rate, is percentage of ex-smokers among "ever daily smokers".

WHO MONICA Project

In the WHO MONICA Project the most commonly used indicators for smoking are prevalence of daily cigarette smoking, and prevalence of ex-smokers. The daily cigarette smoker is a person who reported smoking cigarettes regularly at the time of the survey. The ex-smoker is a person who reported having smoked cigarettes regularly in the past but was not a current smoker at the time of the survey. (23, 24)

Risk factor monitoring in the Netherlands

In the Monitoring Project on Cardiovascular Disease Risk Factors and the MORGEN-project the percentage of smokers, ex-smokers and never-smokers were reported as well as average number of cigarettes smoked by smokeres (5).

Risk factor monitoring in Germany

The German Federal Health Survey 1998 reported the prevalence of never-smoker, ex-smokers, and smokers (unknown whether this includes daily and occasional smokers). In addition, the average cigarette consumption per daily-smoker and the percentage of smokers who had started smoking at age 20 or earlier. All data are reported by sex and age group. (25)

UK National Health Surveys

In the UK National Health Survey several indicators are used to report smoking prevalence in the population. From self-reported data the following indicators are derived (7): current cigarette smoker, ex-regular cigarette smoker and never regular cigarette smoker. Also the average number of cigarettes smoked per day by smokers is reported.

NHANES III

In NHANES III the prevalence of current cigarette smokers was used for reporting of smoking data. The self-reported smoking status was validated by serum cotinine levels (cutpoint > 13 mg/ml). (26)

7.6 Discussion and conclusions

All of the reviewed questionnaires ask about the person's current and past smoking status, but there are differences in the structure, the order, and the wording of the questions. Surveys collected a variable amount of other related information, such as amount of smoking, brand of cigarettes and exposure to environmental tobacco smoke.

Prevalence of daily smoking is probably the most important indicator that all surveys intend to measure. In this respect the questionnaires fell into two categories. In one category were those which focused primarily on cigarette smoking, and took pipe and cigar smoking separately at the end of the questionnaire (MONICA, Netherlands, UK, NHANES). In the other category were the questionnaires which measured directly any type of smoking, and possibly asked about the different forms of smoking at the end of the questionnaire (FINBALT, EUROHIS, WHO). The focus on cigarette smoking  in many of the questionnaires presumably comes from the fact that it is by far the most common form of smoking in Europe, and in many countries practically the only form of smoking. However, all forms of smoking carry a similar risk. In some countries pipe and cigar smoking are common. Furthermore, as a result of intensive antismoking activities, some cigarette smokers tend to switch to cigar or pipe smoking. This justifies the general smoking approach in the relatively new FINBALT and WHO questionnaires for international use. All of the questionnaires also provided information on ex-daily smoking, but many collected this information for cigarette smoking only.

Very little has been published about the validation of the different questionnaires, although biochemical validation of self-reported smoking status was part of many studies. The quality assessment of the data on smoking behavior in the MONICA Project is largely based on assessment of the data, without knowing the true smoking status of the participants.

The importance, or even the usefulness of biochemical markers of smoking in population surveys is not obvious. The problem with thiocyanate and carbon monoxide is their non-specificity. Therefore, more literature exists about the validation of these markers as indicators of smoking than about the validation of questionnaire data using these biomarkers. Cotinine is very specific and sensitive to smoking or use of other nicotine containing products, such as nicotine replacement therapy or smokeless tobacco. If cheaper techniques for its measurement will be developed, it may be an important indicator of exposure to environmental tobacco smoke in the future, because the measurement of environmental tobacco smoke using only a questionnaire is not easy.

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