Objective-To test the feasibility of creating a valid and reliable checklist with the following features: appropriate for assessing both randomised and non-randomised studies; provision of both an overall score for study quality and a profile of scores not only for the quality of reporting, internal validity (bias and confounding) and power, but also for external validity. Design-A pilot version was first developed, based on epidemiological principles, reviews, and existing checklists for randomised studies. Face and content validity were assessed by three experienced reviewers and reliability was determined using two raters assessing 10 randomised and 10 non-randomised studies. Using diVerent raters, the checklist was revised and tested for internal consistency (Kuder-Richardson 20), testretest and inter-rater reliability (Spearman correlation coeYcient and sign rank test; statistics), criterion validity, and respondent burden. Main results-The performance of the checklist improved considerably after revision of a pilot version. The Quality Index had high internal consistency (KR-20: 0.89) as did the subscales apart from external validity (KR-20: 0.54). Test-retest (r 0.88) and inter-rater (r 0.75) reliability of the Quality Index were good. Reliability of the subscales varied from good (bias) to poor (external validity). The Quality Index correlated highly with an existing, established instrument for assessing randomised studies (r 0.90). There was little diVerence between its performance with non-randomised and with randomised studies. Raters took about 20 minutes to assess each paper (range 10 to 45 minutes). Conclusions-This study has shown that it is feasible to develop a checklist that can be used to assess the methodological quality not only of randomised controlled trials but also non-randomised studies. It has also shown that it is possible to produce a checklist that provides a profile of the paper, alerting reviewers to its particular methodological strengths and weaknesses. Further work is required to improve the checklist and the training of raters in the assessment of external validity.

Decreasing exposure to airborne particulates appears to attenuate the decline in lung function related to exposure to PM10. The effects are greater in tests reflecting small-airway function.

OBJECTIVES: The Swiss Cohort Study on Air Pollution and Lung Diseases in Adults (SAPALDIA) was designed to investigate the health effects from long-term exposure to air pollution. METHODS: The health assessment at recruitment (1991) and at the first reassessment (2001-3) consisted of an interview about respiratory health, occupational and other exposures, spirometry, a methacholine bronchial challenge test, end-expiratory carbon monoxide (CO) measurement and measurement for atopy. A bio bank for DNA and blood markers was established. Heart rate variability was measured using a 24-hour ECG (Holter) in a random sample of participants aged 50 years and older. Concentrations of nitrogen dioxide (NO2), sulphur dioxide (SO2), ozone (O3) and particulates in ambient air have been monitored in all study areas since 1991. Residential histories collected over the 11 year follow-up period coupled with GIS modelling will provide individual long-term air pollutant exposure estimates. RESULTS: Of 9651 participants examined in 1991, 8715 could be traced for the cohort study and 283 died. Basic information about health status was obtained for 8047 individuals (86% of alive persons), 6 528 individuals (70%) agreed to the health examination and 5 973 subjects (62%) completed the entire protocol. Non-participants in the reassessment were on average younger than participants and more likely to have been smokers and to have reported respiratory symptoms in the first assessment. Average weight had increased by 5.5 kg in 11 years and 28% of smokers in 1991 had quit by the time of the reassessment. The most powerful approach for studying long-term effects from ambient air pollution on health is the long-term prospective follow-up of well-defined population-based cohorts with well-characterized air pollution exposure information (European Science Foundation 1998). There are currently only five cohort studies in adults, with published results, that address the long-term impact of air pollution (Abbey et al. 1999;Dockery et al. 1993;Finkelstein et al. 2004;Hoek et al. 2002; Pope et al. 2002;. All studies but one are based in the US and three of them (Dockery et al. 1993;Hoek et al. 2002; Pope et al. 2002), have only published findings related to mortality. The relation of longterm exposure to air pollution with respiratory and cardiovascular health and morbidity has yet to be measured in a large prospective cohort study in Europe. The large European Community Respiratory Health Survey (ECRHS) de- Probst-Hensch NM, et al. Follow-up of SAPALDIA 2, 1991-2003 signed to measure natural history and risk factors for respiratory diseases (particularly asthma and allergy) across Europe has recently included air pollution exposure assessment in its protocol (Burney et al. 1994;Hazenkamp-von Arx et al. 2004). However, the Swiss Cohort Study on Air Pollution and Lung Diseases in Adults (SAPALDIA) is the only prospective cohort study of respiratory and cardiovascular health in adults in Europe with detailed individual residential exposure hi...