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The true size of the lung cancer risk from indoor radon: hidden behind a smoke screen?
International Congress Series 1225 (2002) 253 – 258
The true size of the lung cancer risk from indoor radon: hidden behind a smoke screen? Ju¨rgen Conrady, Karl Martin *, Ju¨rgen Lembcke, Horst Martin PreCura Institute for Preventive Medicine, Auguststraße 2, D-16321 Schoenow, Germany
Abstract The estimation of the relative lung-cancer risk (Odds Ratio (OR)) by exposure to radon in dwellings with main emphasis on non-smoking women and control for misspecification of the smoking behaviour was the objective of the Schneeberg study. This case-control study was performed in a highly exposed population to indoor radon from 50 to more than 3000 Bq/m3. The dose – responseanalysis was conducted under consideration of differently accumulated exposures over 30 years. A validation of self-reported cigarette consumption and smoking status by lung cancer cases before and after diagnosis of lung cancer was performed. The misspecification of cigarette consumption and the smoking status was systematically shifted in one direction only: underreporting of cigarettes smoked and denial of the smoking habit. Therefore, results of lung cancer risk estimation from indoor radon in studies with a high proportion of smokers among cases and controls and low exposure levels can easily be explained by misspecification of cigarettes smoked. The presented risk estimation for lung cancer risk from indoor radon with highly exposed non-smoking women resulted in OR not elevated up to 1000 Bq/m3 as a mean value. Only for higher radon values the OR rose steeply up to about 7 with more than 3000 Bq/m3. The results from the study are firstly, that radon is a cause for lung cancer but probably not at the low level as found in most houses and secondly, the problem to control the confounder smoking results in the necessity to conduct epidemiologic radon studies with non-smokers only. D 2002 Elsevier Science B.V. All rights reserved. Keywords: Lung cancer risk; Indoor radon; Smoke screen
1. Study condition and study design A case-control study (Schneeberg study) was performed [1] with female lung cancer cases registered in the East German Cancer Registry from 1952 to 1989 and documented death certificates for lung cancer from 1990 to 1997. Four population controls have been selected for each lung cancer case: two from the cancer registry and two hospital controls *
Corresponding author.
0531-5131/02 D 2002 Elsevier Science B.V. All rights reserved. PII: S 0 5 3 1 - 5 1 3 1 ( 0 1 ) 0 0 5 3 3 - 7
254
J. Conrady et al. / International Congress Series 1225 (2002) 253–258
(other than lung cancer and free from metastases in the lung, illness with no known radon or smoking effect) living at least 25 years in the same area as the cases. Matched sets total: 72 cases, 240 register controls, 48 hospital controls (72/288). Data on smoking behaviour were validated by different methods—self-reports at different times when healthy and when diagnosed for lung cancer, and a purely analytic method. The study area are the two closely located towns Schneeberg and Schlema in Saxony with about 20,000 and 3000 inhabitants, respectively. The study area and its study population have some characteristics that distinguish them from other studies and their populations on the risk from indoor radon. Highly exposed to indoor radon with a wide range of exposure from 50 to >3000 Bq/ m3 as median values. The exposed fraction of the population is with about 30% very high, even when a threshold level for exposed vs. unexposed of 1000 Bq/m3 is applied. The majority of the study population of women are non-smokers. Confounding effects from smoking could be excluded when non-smokers only are analysed. Smoking is the main risk for lung cancer. BEIR VI stated that the lung cancer risk from smoking amounts to 10 – 20 and that from indoor radon amounts to 0.2 –0.3 only. The combination of a weak cause (radon) and a strong confounder (cigarette smoke) makes great demands on the accuracy of measurements of tobacco use. Any misspecification of the smoking habit has extremely serious consequences for risk estimations. This applies to all miners and population studies with high proportions of smokers among cases and controls. The residential mobility of the study population is very low. This is due to the closeness of the population in the Ore Mountains (Erzgebirge) to their home and by political conditions for forty years after WW II in East Germany. The study population is included in a cancer registry since 1953 to the present day. It was (and is for Saxony) mandatory for each doctor to notify the local cancer registry by standardised forms. The completeness of collected incident cases was 95%. The high quality of the cancer registry has been confirmed [2]. The number of probationers included in the Schneeberg study is small. It is due to the small size of the study area with the exceptionally high indoor radon exposure and its small population. The Schneeberg study was concentrated on a high-risk population to establish the true size of the lung cancer risk from indoor radon unbiased by smoking. The highly exposed population can be increased when sub-populations from the region are included for future research. Despite its small size the power of the Schneeberg study is due to its special properties with about 80% over all exposure categories very high. The special characteristics of the population in the study area of the Ore Mountains (Saxony) could make it a new key population in radiation research.
2. Results of the Schneeberg study The risk analysis was conducted by conditional logistic regression and in two different steps—with raw data (smokers, all types of histology and cases without confirmed histology included) and stratified data only (non-smokers and lung cancer histology confirmed). The
J. Conrady et al. / International Congress Series 1225 (2002) 253–258
255
analysis of a possible dose –response relation was conducted after the cumulative radon exposure of the probationers was divided into five exposure categories with reference to the exposure category 0 = OR 1, with < 2.4 106 Bq/m3 or an exposure with at most 50 Bq/m3, adjusted for the year of birth. An increased significant OR can be established by the two forms of analysis in the higher exposure categories only. Below a radon-concentration of 48 106 (Bq h/m3) accordingly 1000 Bq/m3, the OR is not elevated. Significantly elevated OR after both forms of the analysis are detectable at the exposure level of >1500 Bq/m3, power is >90% for the highest exposure category.
3. Validation of the smoking habit A validation of self-reported cigarette consumption and smoking status by lung cancer cases before and after diagnosis of lung cancer was conducted. The misspecification of cigarette consumption and the smoking status was systematically shifted in one direction only:
underreporting of cigarettes smoked; denial of the smoking habit.
Cancer cases reported after diagnosis of lung cancer to be non-smokers vs. 67% of them who were reported to be smokers when healthy. The amount of cigarettes smoked varied considerably when interviewed healthy in comparison to self-reports when lung cancer was diagnosed. About 48% of the cases diminished their amount of cigarettes smoked from more than 10 per day to less than 10 per day. These data where collected individually from routine examinations for lung diseases when healthy and self-reports at the local cancer registry when lung cancer was diagnosed. The results demonstrate that the self-reported smoking behaviour of lung cancer cases that are made at time of diagnosis are biased due to an obvious tendency to repress and minimise their smoking habit. The cases are stressed due to the dangerous nature of their disease and the well known relationship between smoking and lung cancer. This observation is in accordance with several other studies regarding the truce of self-reported amounts of cigarettes smoked and other reports about life style related risk factors [3 –8], alcohol consumption, eating behaviour, exercises, etc. A recent study with healthy individuals about the accurate memory of past events [9] showed for a period of more than 30 years no better results than chance. This makes the control of the influence from smoking on the risk estimate for lung cancer exposure to indoor radon, especially in studies with mainly smokers among cases and controls, very doubtful. Fig. 1 demonstrates how sensitive radon risk estimations react to misspecification of cigarette consumption. The line German Radon Study (GRS, matching region with higher radon exposure [10]) presents a risk estimate for indoor radon. The risk for lung cancer increases from the reference category 0– 50 Bq/m3 with an OR of 1 –1.57 in the exposure category 50 –80 Bq/m3 to the exposure categories 80 –140 Bq/m3 and >140 Bq/m3 with the OR of 1.93 for both categories. Surprisingly, the OR does not follow the monotonous increasing exposure in accordance with LNT in the two highest exposure categories. The
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J. Conrady et al. / International Congress Series 1225 (2002) 253–258
Fig. 1. Radon risk estimation ‘‘German Radon Study’’ (GRS) for lung cancer likely biased by assumed misspecification of cigarettes smoked (1 and >5 cigarettes per day).
lowest curve (one cigarette) presents the lung cancer risk from indoor radon with an assumed misspecification of one cigarette per day. The lung cancer risk of one is already 13% elevated independent from the exposure categories. This elevated risk from misspecification of cigarette consumption becomes wrongly attributed to indoor radon. If the misspecification for daily smoked cigarettes increases to >5 per day (>5 cigarette) the lung cancer risk increases to 75% above the OR of 1, This curve (>5 cigarette) is almost in total agreement with the assumed lung cancer risk from indoor radon in the German Radon Study (GRS) [10]. The quantitative derivation of the uncertainty due to misspecification of the smoking history is presented in Ref. [1]. The results of a lung cancer risk estimation from indoor radon in studies with a high proportion of smokers among cases and controls and low exposure levels can easily be explained by misspecification of cigarettes smoked. A solution to prevent smoking bias in radon studies for the lung cancer risk from radon is the use of non-smoking probationers
Fig. 2. Lung cancer risk estimation in a smoker study with low level of exposure to indoor radon ‘‘German Radon Study’’ (GRS) vs. non-smoker study ‘‘Schneeberg Study’’ (SBS) with high exposure to indoor radon in comparison to LNT.
J. Conrady et al. / International Congress Series 1225 (2002) 253–258
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only. The confounding effect of differences in the estimation of the lung cancer risk between epidemiologic studies with smokers and non-smokers is demonstrated in Fig. 2. Three curves are presented with Fig. 2. GRS is the risk estimate from the German Radon Study [10]. This study contains mostly smokers among cases and not a representative part of smokers among controls. A confounder smoking is statistically controlled so the influence from smoking is seemingly excluded. A confounder is smoking that can be fully controlled without error only when correctly measured. The result from this paper is you cannot measure the quantity of cigarettes smoked over a time period of 20 or 30 years correctly and overcome the inclination of smokers when diagnosed for lung cancer to diminish and even deny their smoking behaviour. An elevated lung cancer risk for instance OR 1.6– 1.9 can therefore easily be explained by faulty self-reports of the smoking behaviour (Fig. 1). The uncontrolled part of the confounder smoking becomes therefore attributed to radon as a cause for lung cancer at the low-dose exposure level. The long curve is the risk estimate for lung cancer from indoor radon with non-smoking women only Schneeberg study (SBS). This curve covers a wide range of radon exposure with median values from about 50 to more than 3000 Bq/m3. No elevated lung cancer risk can be established up to about 1000 Bq/m3 as a mean value. For higher radon values, the OR rises steeply up to an OR of 7 with more than 3000 Bq/m3 indoor radon exposure. The elongated curve (LNT) from the German Radon Study in accordance with LNT shows the increase in lung cancer risk from indoor radon, when its risk calculation might be true. The directly derived lung cancer risk from indoor radon with the Schneeberg study (SBS) is over a wide range of exposure levels not in accordance with the risk estimate from the German Radon Study (GRS). The discrepancies between these two curves are obvious. A possible explanation is an unavoidable smoking bias in the German Radon Study (GRS) and the exposure level that is too low and the exposure range that is too narrow. The shape of the dose –response curve from the Schneeberg study (SBS) contradicts the linear no-threshold theory (LNT). This is interpreted only as a further hint that the LNT might not be true in the low-dose exposure range of indoor radon. Radon is a cause for lung cancer but probably not at the low levels as found in most houses.
4. Conclusion The dominant influence of the smoking behaviour on the lung cancer risk in comparison to the weak influence from indoor radon by the low exposure levels in most population studies and the problem to control the confounding factor smoking results in the necessity to conduct studies with non-smokers. These studies should be performed in key study populations only to test the LNT by epidemiological methods. References [1] J. Conrady, K. Martin, A. Poffijn, M. Tirmarche, J. Lembcke, M.T. Do, H. Martin, High residential radon health effects in Saxony (Schneeberg study). Final Report. Contract No. FI4P-CT95-0027, European Commission, DG XII, Nuclear Fission Safety Programme, August 1999.
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J. Conrady et al. / International Congress Series 1225 (2002) 253–258
[2] G. Enderlein, K. Martin, G. Heuchert, H. Stark, Registerabgleich und Analyse arbeitsbezogener Krebsrisiken mittels Kohortenstudien, Schriftenreihe der Bundesanstalt fu¨r Arbeitsmedizin, Forschung Fb 01 HK 520, Berlin, 1995. [3] E.J. Perez-Stable, B.V. Marin, G. Marin, D.J. Brody, N.L. Bennowitz, Apparent underreporting of cigarette consumption among Mexican American smokers, Am. J. Public Health 80 (1990) 1057 – 1061. [4] R.J. Roskoe, K. Steenland, Lung cancer mortality among non-smoking uranium miners exposed to radon daughters, JAMA 262 (1994) 626 – 633. [5] P. Suadicani, H.O. Hein, Mortality and morbidity of potentially misclassified smokers, Int. J. Epidemiol. 26/ 2 (1997) 321 – 327. [6] A. Mark, R. Klebanoff, R. Levine, J. Clemens, J. DerSimonian, D. Wilkins, Serum cotinine concentration and self-reported smoking during pregnancy, Am. J. Epidemiol. 148 (1998) 259 – 262. [7] P. Dietz, M. Adams, J. Kendrick, M. Mathis, PRAMS Working Group (CDC, Mailstop K35, Atlanta GA), Completeness of ascertainment of prenatal smoking using birth certificates and confidential questionnaires, Variations by maternal attributes and infant birth weight, Am. J. Epidemiol. 148 (1998) 1048 – 1054. [8] A. Hill, J. Roberts, Body mass index: a comparison between self reported and measured height and weight, J. Public Health Med. 20 (1998) 206 – 210. [9] D. Offer, M. Kaiz, I. Kenneth, H. Bennett, The altering of reported experiences, J. Am. Acad. Child Adolesc. Psychiatry 39 (6) (2000) 735 – 742. [10] H.E. Wichmann, L. Kreienbrock, M. Kreuzer, M. Gerken, G. Dingerkus, J. Wellmann, G. Keller, Lungenkrebs durch Radon in der Bundesrepublik Deutschland (WEST), ecomed verlagsgesellschaft, 1998.
The true size of the lung cancer risk from indoor radon: hidden behind a smoke screen? Ju¨rgen Conrady, Karl Martin *, Ju¨rgen Lembcke, Horst Martin PreCura Institute for Preventive Medicine, Auguststraße 2, D-16321 Schoenow, Germany
Abstract The estimation of the relative lung-cancer risk (Odds Ratio (OR)) by exposure to radon in dwellings with main emphasis on non-smoking women and control for misspecification of the smoking behaviour was the objective of the Schneeberg study. This case-control study was performed in a highly exposed population to indoor radon from 50 to more than 3000 Bq/m3. The dose – responseanalysis was conducted under consideration of differently accumulated exposures over 30 years. A validation of self-reported cigarette consumption and smoking status by lung cancer cases before and after diagnosis of lung cancer was performed. The misspecification of cigarette consumption and the smoking status was systematically shifted in one direction only: underreporting of cigarettes smoked and denial of the smoking habit. Therefore, results of lung cancer risk estimation from indoor radon in studies with a high proportion of smokers among cases and controls and low exposure levels can easily be explained by misspecification of cigarettes smoked. The presented risk estimation for lung cancer risk from indoor radon with highly exposed non-smoking women resulted in OR not elevated up to 1000 Bq/m3 as a mean value. Only for higher radon values the OR rose steeply up to about 7 with more than 3000 Bq/m3. The results from the study are firstly, that radon is a cause for lung cancer but probably not at the low level as found in most houses and secondly, the problem to control the confounder smoking results in the necessity to conduct epidemiologic radon studies with non-smokers only. D 2002 Elsevier Science B.V. All rights reserved. Keywords: Lung cancer risk; Indoor radon; Smoke screen
1. Study condition and study design A case-control study (Schneeberg study) was performed [1] with female lung cancer cases registered in the East German Cancer Registry from 1952 to 1989 and documented death certificates for lung cancer from 1990 to 1997. Four population controls have been selected for each lung cancer case: two from the cancer registry and two hospital controls *
Corresponding author.
0531-5131/02 D 2002 Elsevier Science B.V. All rights reserved. PII: S 0 5 3 1 - 5 1 3 1 ( 0 1 ) 0 0 5 3 3 - 7
254
J. Conrady et al. / International Congress Series 1225 (2002) 253–258
(other than lung cancer and free from metastases in the lung, illness with no known radon or smoking effect) living at least 25 years in the same area as the cases. Matched sets total: 72 cases, 240 register controls, 48 hospital controls (72/288). Data on smoking behaviour were validated by different methods—self-reports at different times when healthy and when diagnosed for lung cancer, and a purely analytic method. The study area are the two closely located towns Schneeberg and Schlema in Saxony with about 20,000 and 3000 inhabitants, respectively. The study area and its study population have some characteristics that distinguish them from other studies and their populations on the risk from indoor radon. Highly exposed to indoor radon with a wide range of exposure from 50 to >3000 Bq/ m3 as median values. The exposed fraction of the population is with about 30% very high, even when a threshold level for exposed vs. unexposed of 1000 Bq/m3 is applied. The majority of the study population of women are non-smokers. Confounding effects from smoking could be excluded when non-smokers only are analysed. Smoking is the main risk for lung cancer. BEIR VI stated that the lung cancer risk from smoking amounts to 10 – 20 and that from indoor radon amounts to 0.2 –0.3 only. The combination of a weak cause (radon) and a strong confounder (cigarette smoke) makes great demands on the accuracy of measurements of tobacco use. Any misspecification of the smoking habit has extremely serious consequences for risk estimations. This applies to all miners and population studies with high proportions of smokers among cases and controls. The residential mobility of the study population is very low. This is due to the closeness of the population in the Ore Mountains (Erzgebirge) to their home and by political conditions for forty years after WW II in East Germany. The study population is included in a cancer registry since 1953 to the present day. It was (and is for Saxony) mandatory for each doctor to notify the local cancer registry by standardised forms. The completeness of collected incident cases was 95%. The high quality of the cancer registry has been confirmed [2]. The number of probationers included in the Schneeberg study is small. It is due to the small size of the study area with the exceptionally high indoor radon exposure and its small population. The Schneeberg study was concentrated on a high-risk population to establish the true size of the lung cancer risk from indoor radon unbiased by smoking. The highly exposed population can be increased when sub-populations from the region are included for future research. Despite its small size the power of the Schneeberg study is due to its special properties with about 80% over all exposure categories very high. The special characteristics of the population in the study area of the Ore Mountains (Saxony) could make it a new key population in radiation research.
2. Results of the Schneeberg study The risk analysis was conducted by conditional logistic regression and in two different steps—with raw data (smokers, all types of histology and cases without confirmed histology included) and stratified data only (non-smokers and lung cancer histology confirmed). The
J. Conrady et al. / International Congress Series 1225 (2002) 253–258
255
analysis of a possible dose –response relation was conducted after the cumulative radon exposure of the probationers was divided into five exposure categories with reference to the exposure category 0 = OR 1, with < 2.4 106 Bq/m3 or an exposure with at most 50 Bq/m3, adjusted for the year of birth. An increased significant OR can be established by the two forms of analysis in the higher exposure categories only. Below a radon-concentration of 48 106 (Bq h/m3) accordingly 1000 Bq/m3, the OR is not elevated. Significantly elevated OR after both forms of the analysis are detectable at the exposure level of >1500 Bq/m3, power is >90% for the highest exposure category.
3. Validation of the smoking habit A validation of self-reported cigarette consumption and smoking status by lung cancer cases before and after diagnosis of lung cancer was conducted. The misspecification of cigarette consumption and the smoking status was systematically shifted in one direction only:
underreporting of cigarettes smoked; denial of the smoking habit.
Cancer cases reported after diagnosis of lung cancer to be non-smokers vs. 67% of them who were reported to be smokers when healthy. The amount of cigarettes smoked varied considerably when interviewed healthy in comparison to self-reports when lung cancer was diagnosed. About 48% of the cases diminished their amount of cigarettes smoked from more than 10 per day to less than 10 per day. These data where collected individually from routine examinations for lung diseases when healthy and self-reports at the local cancer registry when lung cancer was diagnosed. The results demonstrate that the self-reported smoking behaviour of lung cancer cases that are made at time of diagnosis are biased due to an obvious tendency to repress and minimise their smoking habit. The cases are stressed due to the dangerous nature of their disease and the well known relationship between smoking and lung cancer. This observation is in accordance with several other studies regarding the truce of self-reported amounts of cigarettes smoked and other reports about life style related risk factors [3 –8], alcohol consumption, eating behaviour, exercises, etc. A recent study with healthy individuals about the accurate memory of past events [9] showed for a period of more than 30 years no better results than chance. This makes the control of the influence from smoking on the risk estimate for lung cancer exposure to indoor radon, especially in studies with mainly smokers among cases and controls, very doubtful. Fig. 1 demonstrates how sensitive radon risk estimations react to misspecification of cigarette consumption. The line German Radon Study (GRS, matching region with higher radon exposure [10]) presents a risk estimate for indoor radon. The risk for lung cancer increases from the reference category 0– 50 Bq/m3 with an OR of 1 –1.57 in the exposure category 50 –80 Bq/m3 to the exposure categories 80 –140 Bq/m3 and >140 Bq/m3 with the OR of 1.93 for both categories. Surprisingly, the OR does not follow the monotonous increasing exposure in accordance with LNT in the two highest exposure categories. The
256
J. Conrady et al. / International Congress Series 1225 (2002) 253–258
Fig. 1. Radon risk estimation ‘‘German Radon Study’’ (GRS) for lung cancer likely biased by assumed misspecification of cigarettes smoked (1 and >5 cigarettes per day).
lowest curve (one cigarette) presents the lung cancer risk from indoor radon with an assumed misspecification of one cigarette per day. The lung cancer risk of one is already 13% elevated independent from the exposure categories. This elevated risk from misspecification of cigarette consumption becomes wrongly attributed to indoor radon. If the misspecification for daily smoked cigarettes increases to >5 per day (>5 cigarette) the lung cancer risk increases to 75% above the OR of 1, This curve (>5 cigarette) is almost in total agreement with the assumed lung cancer risk from indoor radon in the German Radon Study (GRS) [10]. The quantitative derivation of the uncertainty due to misspecification of the smoking history is presented in Ref. [1]. The results of a lung cancer risk estimation from indoor radon in studies with a high proportion of smokers among cases and controls and low exposure levels can easily be explained by misspecification of cigarettes smoked. A solution to prevent smoking bias in radon studies for the lung cancer risk from radon is the use of non-smoking probationers
Fig. 2. Lung cancer risk estimation in a smoker study with low level of exposure to indoor radon ‘‘German Radon Study’’ (GRS) vs. non-smoker study ‘‘Schneeberg Study’’ (SBS) with high exposure to indoor radon in comparison to LNT.
J. Conrady et al. / International Congress Series 1225 (2002) 253–258
257
only. The confounding effect of differences in the estimation of the lung cancer risk between epidemiologic studies with smokers and non-smokers is demonstrated in Fig. 2. Three curves are presented with Fig. 2. GRS is the risk estimate from the German Radon Study [10]. This study contains mostly smokers among cases and not a representative part of smokers among controls. A confounder smoking is statistically controlled so the influence from smoking is seemingly excluded. A confounder is smoking that can be fully controlled without error only when correctly measured. The result from this paper is you cannot measure the quantity of cigarettes smoked over a time period of 20 or 30 years correctly and overcome the inclination of smokers when diagnosed for lung cancer to diminish and even deny their smoking behaviour. An elevated lung cancer risk for instance OR 1.6– 1.9 can therefore easily be explained by faulty self-reports of the smoking behaviour (Fig. 1). The uncontrolled part of the confounder smoking becomes therefore attributed to radon as a cause for lung cancer at the low-dose exposure level. The long curve is the risk estimate for lung cancer from indoor radon with non-smoking women only Schneeberg study (SBS). This curve covers a wide range of radon exposure with median values from about 50 to more than 3000 Bq/m3. No elevated lung cancer risk can be established up to about 1000 Bq/m3 as a mean value. For higher radon values, the OR rises steeply up to an OR of 7 with more than 3000 Bq/m3 indoor radon exposure. The elongated curve (LNT) from the German Radon Study in accordance with LNT shows the increase in lung cancer risk from indoor radon, when its risk calculation might be true. The directly derived lung cancer risk from indoor radon with the Schneeberg study (SBS) is over a wide range of exposure levels not in accordance with the risk estimate from the German Radon Study (GRS). The discrepancies between these two curves are obvious. A possible explanation is an unavoidable smoking bias in the German Radon Study (GRS) and the exposure level that is too low and the exposure range that is too narrow. The shape of the dose –response curve from the Schneeberg study (SBS) contradicts the linear no-threshold theory (LNT). This is interpreted only as a further hint that the LNT might not be true in the low-dose exposure range of indoor radon. Radon is a cause for lung cancer but probably not at the low levels as found in most houses.
4. Conclusion The dominant influence of the smoking behaviour on the lung cancer risk in comparison to the weak influence from indoor radon by the low exposure levels in most population studies and the problem to control the confounding factor smoking results in the necessity to conduct studies with non-smokers. These studies should be performed in key study populations only to test the LNT by epidemiological methods. References [1] J. Conrady, K. Martin, A. Poffijn, M. Tirmarche, J. Lembcke, M.T. Do, H. Martin, High residential radon health effects in Saxony (Schneeberg study). Final Report. Contract No. FI4P-CT95-0027, European Commission, DG XII, Nuclear Fission Safety Programme, August 1999.
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J. Conrady et al. / International Congress Series 1225 (2002) 253–258
[2] G. Enderlein, K. Martin, G. Heuchert, H. Stark, Registerabgleich und Analyse arbeitsbezogener Krebsrisiken mittels Kohortenstudien, Schriftenreihe der Bundesanstalt fu¨r Arbeitsmedizin, Forschung Fb 01 HK 520, Berlin, 1995. [3] E.J. Perez-Stable, B.V. Marin, G. Marin, D.J. Brody, N.L. Bennowitz, Apparent underreporting of cigarette consumption among Mexican American smokers, Am. J. Public Health 80 (1990) 1057 – 1061. [4] R.J. Roskoe, K. Steenland, Lung cancer mortality among non-smoking uranium miners exposed to radon daughters, JAMA 262 (1994) 626 – 633. [5] P. Suadicani, H.O. Hein, Mortality and morbidity of potentially misclassified smokers, Int. J. Epidemiol. 26/ 2 (1997) 321 – 327. [6] A. Mark, R. Klebanoff, R. Levine, J. Clemens, J. DerSimonian, D. Wilkins, Serum cotinine concentration and self-reported smoking during pregnancy, Am. J. Epidemiol. 148 (1998) 259 – 262. [7] P. Dietz, M. Adams, J. Kendrick, M. Mathis, PRAMS Working Group (CDC, Mailstop K35, Atlanta GA), Completeness of ascertainment of prenatal smoking using birth certificates and confidential questionnaires, Variations by maternal attributes and infant birth weight, Am. J. Epidemiol. 148 (1998) 1048 – 1054. [8] A. Hill, J. Roberts, Body mass index: a comparison between self reported and measured height and weight, J. Public Health Med. 20 (1998) 206 – 210. [9] D. Offer, M. Kaiz, I. Kenneth, H. Bennett, The altering of reported experiences, J. Am. Acad. Child Adolesc. Psychiatry 39 (6) (2000) 735 – 742. [10] H.E. Wichmann, L. Kreienbrock, M. Kreuzer, M. Gerken, G. Dingerkus, J. Wellmann, G. Keller, Lungenkrebs durch Radon in der Bundesrepublik Deutschland (WEST), ecomed verlagsgesellschaft, 1998.