References and notes for Section 2
1. The 5th centile is the value below which 5% of a healthy population lie; similarly, 2.5% of a healthy population lie below the 2.5th centile. The text explains this further.
2. Spirometry is measurement of lung function. See chapter 1.
3. Gray L, Leyland A. 'Respiratory health.' Chapter 8 in: Bromley C, Givens L (eds). Scottish Health Survey 2010. Volume 1. Main report. Edinburgh: Scottish Government, 2011. www.scotland.gov.uk/Publications/2011/09/27084018/58
4. Spirometry is the measurement of lung function.
5. A bronchodilator is a substance that dilates the passages in the airway of the respiratory tract, decreasing resistance in the respiratory airway and increasing airflow to the lungs. Bronchodilators were not used in the SHeS as nurses would not be able to administer this medication to survey participants without a prescription.
6. Stanojevic S, Wade A, Stocks J et al. Reference ranges for spirometry across all ages: a new
7. approach. Am J Respir Crit Care Med. 2008;177:253-60..
8. The z-score (also called the standard deviation score, or SDS) equals the measured value minus the predicted value, divided by the between-subject standard deviation. By definition in healthy subjects, the mean z-score should equal 0 (and the standard deviation should equal 1), with 95% of healthy subjects falling within ±1.96 standard deviations from the mean. With spirometry, the distribution of interest is one-sided, i.e. the focus is only on those with results below the predicted value.
9. Centiles show the position of parameters within a statistical distribution in a normal (healthy) population. If a parameter is on the 5th centile, this means that for every 100 people, 5 would be expected to be at or below that level and 95 above.
10. By definition, 5% of a 'normal' population will be deemed to fall outside the normal ('healthy') range of any value. In clinical situations, the 5th centile (z-score less than -1.64) is generally considered the lower limit of normal (LLN) for spirometry as patients generally have symptoms or signs indicating a higher likelihood of disease. There are two arguments for considering only those below the 2.5th centile (z-score less than -1.96) as abnormal in this report. First, this is a general population sample, so fewer would be expected to have abnormal values than in a clinical sample. Secondly, when interpreting two or more tests that are physiologically related using the 5% threshold as abnormal results in 10.5% of healthy adults having at least one of FEV1, FVC, or FEV1/FVC falling in the bottom 5% of values.(J.Stocks, personal communication).
11. Participants with asthma or other respiratory conditions were included in the analysis. When the regressions were repeated excluding those with asthma, the odds ratios and significance values for the other variables remained very similar.
12. Participants who currently smoked were asked how many cigarettes they smoked per weekday and weekend day. This was multiplied by the number of years since they first started smoking, to produce the number of packyears. Participants who had stopped smoking were asked how many cigarettes they used to smoke on an average day, and this was multiplied by their number of years smoking (age stopped smoking minus age started). Those who said that they had never smoked, or only occasionally smoked were assigned a value of 0.
13. National Institute for Health and Care Excellence. Management of chronic obstructive pulmonary disease in adults in primary and secondary care (partial update). Clinical guidance CG101. London, NICE, 2010. http://guidance.nice.org.uk/CG101
14. Quanjer PH, Stanojevic S, Cole TJ, et al. Multi-ethnic reference values for spirometry for the 3-95 year age range: the global lung function 2012 equations. Eur Resp J. erj00803-2012.
16. Quanjer PH, Stanojevic S, Cole TJ, et al. Ethnic-specific all-age prediction equations for spirometry: The ERS Global Lungs Initiative. Am J Respir Crit Care Med. 2011;83:A2177.
17. Not all ethnic groups are covered by the new multi-ethnicity equations, due to paucity of data from some ethnic groups. In particular, references for Indian subcontinent populations are not provided; the reference equations for Chinese participants are divided geographically but we do not know from which part of China respondents may originate. The reference equations are provided as follows:
18. Caucasian: Europe, Israel, Australia, USA, Canada, Mexican Americans, Brazil, Chile, Mexico, Uruguay, Venezuela, Algeria, Tunisia
19. Black African American
20. South East Asian: Thailand, Taiwan and China (including Hong Kong) south of the Huaihe River and Qinling Mountains
21. North East Asian: Korea and China north of the Huaihe River and Qinling Mountains.
22. Scholes S, Moody A, Mindell JS. Estimating population prevalence of potential airflow obstruction using different spirometric criteria: a pooled cross-sectional analysis of persons aged 40-95 years in England and Wales. Accepted by BMJ Open.
23. Leon DA, Morton S, Cannegieter S, McKee M. Understanding the health of Scotland's population in an international context. A review of current approaches, knowledge and recommendations for new research directions. 2nd edition. London, LSHTM, 2003. www.scotpho.org.uk/publications/reports-and-papers/500-scottish-mortality-in-a-european-context-1950-2000-an-analysis-of-comparative-mortality-trends-
24. Hole DJ, Watt GC, Davey-Smith G, Hart CL, Gillis CR, Hawthorne VM. Impaired lung function and mortality risk in men and women: findings from the Renfrew and Paisley prospective population study.BMJ. 1996;313:711-5; discussion 715-6.
25. Census data shows that in 1951 the occupations of working men and women in Scotland differed greatly. For men the main occupations were metal work (16%) clerical work (13%) other production (12%) transport (11%) and agriculture (10%); whereas almost half of working women were in clerical (34%) or domestic service (15%). Source: The Scottish Economy: A Statistical Account of Scottish Life By University of Glasgow p41.
26. Beelen R, Raaschou-Nielsen O, Staffogia M et al. Effects of long-term exposure to air pollution on natural-cause mortality: an analysis of 22 European cohorts within the multicentre ESCAPE project Lancet. 2014:383:9919
Read codes are the recommended national standard coding system in Scottish general practices for recording clinical information (signs, symptoms, diagnoses or activities). More information on Read codes can be found on the Health and Social Care Information website. http://www.isdscotland.org/Health-Topics/General-Practice/GP-Consultations/Grouping-clinical-codes.asp
Email: Julie Landsberg
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