The data are from the West of Scotland Twenty‐07 study, a longitudinal study that was set up to investigate the social patterning of health among three cohorts, aged around 15, 35, and 55 years when first interviewed in 1987/88. Each of the three cohorts comprised approximately 1000 people. Respondents were drawn from clustered random samples from the Central Clydeside Conurbation, a socially varied but mainly urban area centred on the city of Glasgow. The samples were found to be broadly representative of the populations from which they were drawn, using 1991 census data.12
The participants are being followed up (approximately every four years) using face to face interviews and postal questionnaires. The interviews are conducted by trained nurses, usually in the participants' homes. Further details on the sample and methods are available elsewhere.13,14
This analysis is limited to data from the oldest cohort collected in 1990/91 when 858 individuals were reinterviewed when they were approximately 58 years old. This wave of data collection included a wide range of measures of disability, self reported health, and sociodemographic factors. These measures were repeated at subsequent contact with the respondents in 1995 (aged 62 years). The majority of the results presented are from the 1990/91 data, as this wave of data collection had the greatest number of respondents and the prevalence of joint pain was very similar for respondents at ages 58 and 62 years.
Respondents were presented with a basic diagram of the human skeleton (a stick person) and were asked for each joint ‘Do you regularly suffer from any swelling, pain or stiffness?'. Data were collected on the neck, back, and separately for the right and left sides of the body for shoulders, elbows, wrists, hand/fingers, hips, knees, ankle, and feet/toes. Respondents were included as having joint problems if they recorded having slight, moderate, or severe pain in either the left or the right joint.
Body mass index
Nurse interviewers recorded the standing height and weight of participants using a stadiometer and scales which were regularly calibrated. Body mass index (BMI) was calculated (kg/m2
) and obese people were classified as those with a BMI greater than 30 kg/m2
. A categorical variable was also generated for BMI (<20 kg/m2
, >20 to
, >25 to <30 kg/m2
) to assess any dose–response relation between BMI and joint pain.
Respondents were asked if they ever smoked tobacco (including pipe, cigars, and roll‐ups as well as manufactured cigarettes). Study participants were divided into never smokers, ex‐smokers, or current smokers. For some of the analyses these categories were collapsed into current versus previous/never smokers.
Respondents were asked to report the number of units of alcohol they drank each day over the previous week, reporting separately for beer/lager/cider, wine, fortified wine, spirits, and other forms of alcohol. Overall alcohol intake for the week was calculated for each of the subtypes of alcohol and the total number of units for all forms of alcohol.
Social class was measured using the Registrar General's occupational social class categories based on the longest held occupation of the head of household (I, professional; II, managerial; IIInm, skilled non‐manual; IIIm, skilled manual; IV, semiskilled manual; V, unskilled manual). Common workplace exposures were also measured, including how many years the respondent had undertaken heavy manual work, frequent bending, and exposure to vibrations (for example, drilling). Data were categorised into none compared with one or more years of exposure. More detail on the measurement of workplace exposures has been reported elsewhere.15
The relation between joint pain and each risk factor was assessed using t tests, χ2 tests, and univariable regression. Multiple logistic regression was used to assess the association between joint pain (any joint pain on either the left or the right side of the body) at each site and obesity, smoking, and total weekly alcohol intake, with adjustment for potential confounding factors (sex, social class, and occupational exposures). All analysis were conducted using STATA 7.
Initial ethical approval for the study was given in 1987 by the ethics subcommittee of the West of Scotland Medical Committee. Each subsequent set of contacts has been approved by the University of Glasgow's ethics committee for non‐clinical research involving human subjects. The study follows ethical principles as set out in the Medical Research Council's ethics and best practice guidelines.