In 1966, 1972, 1977, 1982, 1989, 1999, 2006-10, and 2014-16, study members were asked the MRC questionnaire on respiratory symptoms (MRCQ).

The MRCQ consists of questions on coughing, phlegm, breathlessness, wheezing and chest illnesses.¹⁾

Details of the questions and variable names resulting from the MRCQ can be seen below.
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Lung function was first measured in 1982, 1989 and 1999. At each timepoint, peak expiratory flow rate (PEFR) was used.

At ages 43 (1989), 53 (1999), 60-64 (2006-10), and 68-70 (2014-16) years forced expiratory volume in one second (FEV1) and forced vital capacity (FVC) were also measured. Three measures were used at 43, 60-64 and 68-70 years and two measures at 53 years. It was also recorded whether the technique for each blow was satisfactory.

Recommended measures of FEV1 and FVC were derived using the American Thoracic Society (ATS) criteria, firstly removing those values where the technique was judged not to be satisfactory then taking the maximum of the two qualifying measures at 53 years and the three qualifying measures at other ages. Impossible values were removed.