Longitudinal versus cross-sectional data
There is sufficient evidence (ref. 1) that age-related trends in cross-sectional studies of lung function differ from those found in longitudinal investigations. There are various explanations for this.
- A selection effect occurs, i.e. the weakest individuals die at an early age, so that increasingly the older subjects in the population represent a positive selection (e.g. with the most favorable lung function).
- A cohort effect may be involved, i.e. that persons born for example 50 years ago had a different lung development during growth than those born 20 years ago. Infectious diseases, nutrition, smoking during gestation, better survival after premature birth, exposure to environmental factors, socio-economic status (which determines bodily development in early life and leads to secular trends in body size and pulmonary function), growing up at altitude, and possibly other environmental factors, etc. might all leave their marks so that the lung function of a 40 yr old person born in 1920 would be different from that in a 40 yr old person born in 1950.
- In a cross-sectional study measurements may have been influenced by seasonal and other climatological factors, whereas in longitudinal studies carried out over a sufficient time span such chance events would tend to average out.
- Technical problems cannot be excluded. Unfortunately the equipment used may still play a role: it is far from easy to properly take into account the effects of gas temperature, humidity and gas composition in calibrating equipment, and even more difficult to do this reproducibly.
Implicit in most studies is that the age-related decline in lung function in adults is attributable to the effect of aging on the lung. However, there is some evidence that it may also be related to changes in body mass; in follow-up studies in males (ref. 2) a 1 kg weight gain has been found to account for a reduction in FEV1 of between 13.9 and 23 mL. However, a higher birth weight is associated with a higher adult FEV1 and FVC. This is consistent with the finding that waist circumference is negatively associated with FEV1 and FVC.
|Ref. 1 - Cross-sectional versus longitudinal data|
|1||Glindmeyer HW, Diem JE, Jones RN, Weill H. Non-comparability of longitudinally and cross-sectionally determined annual change in spirometry. Am Rev Respir Dis 1982; 125: 544-548.|
|2||Burrows B, Lebowitz MD, Casmilli AE, Knudson RJ. Longitudinal changes in forced expiratory volume in one second in adults. Methodologic considerations and findings in healthy nonsmokers. Am Rev Respir Dis 1986; 133: 974-980.|
|3||Jedrychowski W, Krzyzanowski M, Wysocki M. Changes in lung function determined longitudinally compared with decline assessed cross-sectionally. The Cracow study. Eur J Epidemiol 1986; 2: 134-138.|
|4||Vollmer WM, Johnson LR, McCamant LE, Buist AS. Longitudinal versus cross-sectional estimation of lung function decline--further insights. Stat Med 1988; 7: 685-696.|
|5||Ware JH, Dockery DW, Louis TA, Xu XP, Ferris BG Jr, Speizer FE. Longitudinal and cross-sectional estimates of pulmonary function decline in never-smoking adults. Am J Epidemiol 1990; 132: 685-700.|
|6||Vollmer WM. Reconciling cross-sectional with longitudinal observations on annual decline. Occup Med 1993; 8: 339-351.|
|4||Van Pelt W, Borsboom GJJM, Rijcken B, Schouten JP, van Zomeren BC, Quanjer PhH. Discrepancies between longitudinal and cross-sectional change in ventilatory function in 12 years of follow-up. Am J Respir Crit Care Med 1994; 149: 1218-1226.|
|7||Xu X, Laird N, Dockery DW, Schouten JP, Rijken B, Weiss ST. Age, period, and cohort effects on pulmonary function in a 24-year longitudinal study. Am J Epidemiol 1995; 141: 554-566.|
|8||Wang ML, McCabe L, Hankinson JL, Shamssain MH, Gunel E, Lapp NL, Banks DE. Longitudinal and cross-sectional analyses of lung function in steelworkers. Am J Respir Crit Care Med 1996; 153: 1907-1913.|
|9||Kerstjens HAM, Rijcken B, Schouten JP, Postma DS. Decline of FEV1 by age and smoking status: facts, figures and fallacies. Thorax 1997; 52: 820-827. (Review article)|
|10||Wang M-L, Petsonk EL. Repeated measures of FEV1 over six to twelve months: what change is abnormal? J Occup Environ Med 2004; 46: 591–595.|
|11||Hnizdo E, Sircar K, Yan T, Harber P, Fleming J, Glindmeyer HW. Limits of longitudinal decline for the interpretation of annual changes in FEV1 in individuals. Occup Environ Med 2007; 64: 701–707.|
|12||Quanjer PH, Borsboom GJJM, Kivastik J, Merkus PJFM, Hankinson JL, Houthuijs D, Brunekreef B, Ihorst G, Kühr J. Cross-sectional and longitudinal spirometry in children and adolescents: interpretative strategies. Am J Respir Crit Care Med 2008; 178: 1262–1270.|
|13||Tanner, J.M., 1986. Growth as a target-seeking function: catch-up and -down growth in man. In: Falkner, F., Tanner, J.M. (Eds.), Human Growth: A Comprehensive Treatise, vol. 2. Plenum Press, New York, pp. 171–209.|
|14||Cole TJ. The secular trend in human physical growth: a biological view. Econ Hum Biol 2003; 1: 161–168.|
|12||Sitarama Raju P, Prasad KVV, Venkata Ramana Y, et al. Influence of socioeconomic status on lung function and prediction equations in Indian children. Pediatr Pulmonol 2005; 39: 528–536.|
|15||Harik-Khan RFI, Muller DC, Wise RA. Racial difference in lung function in African-American and white children: effect of anthropometric, socioeconomic, nutritional, and environmental factors. Am J Respir Epidemiol 2004; 160: 893–900.|
|16||Whitrow MJ, Harding S. Ethnic differences in adolescent lung function. Anthropometric, socioeconomic, and psychological factors. Am J Respir Crit Care Med 2008; 177: 1262–1267.|
|Ref. 2 - Change in body mass and in FEV1|
|1||Cotes JE, Gilson JC. Effect of inactivity, weight gain and antitubercular chemotherapy upon lung function in working coal-miners. Ann Occup Hyg 1967; 10: 327-335.|
|2||Bande J, Clément J, van de Woestijne KP. The influence of smoking habits and body weight on vital capacity and FEV1 in male airforce personnel: a longitudinal and cross-sectional analysis. Am Rev Respir Dis 1980; 122: 781-790.|
|3||Chen Y, Horne SL, Dosman JA. Body weight and weight gain related to pulmonary function decline in adults: a six year follow up study. Thorax 1993; 48: 375-380.|
|4||Chinn DJ, Cotes JE, Reed JW. Longitudinal effects of change in body mass on measurements of ventilatory capacity. Thorax 1996; 51: 699-704.|
|5||Beverley AC, Blizzard CL, Schmidt MD, Walters EH, Dwyer T, Venn AJ. Longitudinal associations of adiposity with adult lung function in the Childhood Determinants of Adult Health (CDAH) study. Obesity 2011; 19; 2069-2075.|
|6||Canoy D, Pekkanen J, Elliott P, Pouta A, Laitinen J, Hartikainen A-L, Zitting P, Patel S, Little MP, Järvelin M-R. Early growth and adult respiratory function in men and women followed from the fetal period to adulthood. Thorax 2007;62:396-402.|
|7||Chen Y, Rennie D, Cormier YF, Dosman J. Waist circumference is associated with pulmonary function in normal-weight, overweight, and obese subjects. Am J Clin Nutr 2007; 85: 35-39.|