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Am J Public Health. 1993 Sep;83(9):1251-7.

Error in smoking measures: effects of intervention on relations of cotinine and carbon monoxide to self-reported smoking. The Lung Health Study Research Group.

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Department of Internal Medicine, University of Manitoba, Winnipeg, Canada.



Sources of measurement error in assessing smoking status are examined.


The Lung Health Study, a randomized trial in 10 clinical centers, includes 3923 participants in a smoking cessation program and 1964 usual care participants. Smoking at first annual follow-up was assessed by salivary cotinine, expired air carbon monoxide, and self-report. Each of these measures is known to contain some error. Sensitivity and specificity were calculated by comparing a biochemical measure with self-report to produce an undifferentiated estimate of error. Classification error rates due to imprecision of the biochemical measures and to the error in self-report were estimated separately.


For cotinine compared with self-report, the sensitivity was 99.0% and the specificity 91.5%. For carbon monoxide compared with self-report, the sensitivity was 93.7% and the specificity 87.2%. The classification error attributed to self-report, estimated by comparing the results from intervention and control groups, was associated with the responses of 3% and 5% of participants, indicating a small but significant bias toward a socially desirable response.


In absolute terms in these data, both types of error were small.

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