Relationship of the loose cough sign to daily sputum volume. Observer variation in its detection.

Evidence of overproduction of sputum, the essential diagnostic feature of chronic bronchitis, is usually sought in epidemiological surveys by questionnaire. This approach is inevitably subjective. A valid objective sign of sputum production would be of value, both as an independent index of chronic bronchitis and as a supplement to the history. Elmes, Dutton, and Fletcher (1959) introduced the measurement of morning sputum volume, but this technique requires co-operation from the subject, may have a high lapse rate, and is open to falsification. Various sources of bias, social, political, and economic, may 4-infuence the results obtained from either the history or sputum collection, particularly in occupational surveys. For the past 12 years it has been the practice in this unit to supplement the information obtained from questionnaires by asking the subject .to take a deep breath and cough; the cough is recorded as 'loose' (productive) or 'dry' (unproductive) as judged by ear. This paper describes two studies of the relationship between the presence of a loose cough, as defined above, and the daily sputum vdlume, and provides information on inter-observer variation in the detection of the sign.