The purpose of this survey was to evaluate the effects of smoking and occupational exposures on the decline in forced expiratory volume in one second (FEV1), and the presence of airflow limitation (FEV1 x100/forced vital capacity (FVC) being
Comment In: Eur Respir J. 1993 Sep;6(8):1088-98224120
We examined the effects from subjects, technicians and spirometers on within-session variability in successful recordings of forced expiratory volume in 1 second (FEV1) and forced vital capacity (FVC) in 4989 asymptomatic never-smoking men. All eligible men aged 30-46 years living in western Norway (n = 45,380) were invited to a cross-sectional community survey. Information on respiratory symptoms, smoking habits and occupational exposures was obtained from a self-administered questionnaire. Three successful FEV1 and FVC recordings were obtained in 26,368 attendants using three dry-wedge bellow spirometers operated by 10 different technicians. Within-subject standard deviation (SD) from three recordings of FEV1 and FVC was on average 102 and 106 ml, respectively, and increased with height (14 and 17 ml, respectively, per 10 cm) and body mass index (BMI) (11 and 14 ml, respectively, per 5 kg m-2). Between-subject SD of the mean of three FEV1 and FVC recordings was 591 and 754 ml, respectively, and increased in groups of increasing height (43 and 40 ml, respectively, per 10 cm). Small, but significant, differences were observed between technicians in within-subject SD and in levels of FEV1 and FVC. Homogeneity of between-subject variability, necessary for linear regression analysis, was obtained using FEV1 and FVC divided by height squared. In conclusion, within-subject variability in three successful spirometric recordings was small, but dependent on height and BMI of the subjects as well as technician performance. The observed heterogeneity in between-subject variation in FEV1 and FVC levels disappeared when each variable was divided by height squared. Novel multiple linear regression equations for FEV1/height2 and FVC/height2 were developed to be used in evaluating the effects from occupational airborne exposures in Nordic men aged 30-46 years.
We have examined the time trends in multiple sclerosis incidence over the past four decades from 1950 to 1991 in Møre and Romsdal County, Norway. Incidence rates by year of birth, year of onset and year of diagnosis according to sex, age and clinical course were studied. All patients with multiple sclerosis diagnosed by August 1992 were included, giving a total of 419 patients (171 men, 248 women) with onset of multiple sclerosis in the period 1950-91. Mean age at onset was 33.2 years, and mean age at diagnosis was 39.2 years. The incidence rate by year of onset increased from 2.87 per 100 000 in the period 1950-54 (men 3.06, women 2.67) to 5.57 per 100 000 in 1985-91 (men 3.75, women 7.94) (P
In previous studies of female cancer risk, we introduced a new method for circumventing the problem of collinearity in age-adjusted analysis of the joint effects of age at birth and time since birth. The basic idea was to estimate the pure age effect considering nulliparous women, assuming that the age effect is common to all women. However, risk estimates for attained age obtained in this manner may suffer from bias, in particular in small data sets, which may in turn influence risk estimates for reproductive factors among parous women. Certain factors possibly affecting cancer risk among nulliparous women only, for instance biological infertility, might also introduce bias. The purpose of this paper is to investigate the accuracy of risk estimates obtained by the joint approach, and to reveal the extent of bias in traditional separate age-adjusted analyses of age at birth or time since birth among parous women. Results are based on analyses of simulated data sets reflecting reproductive and demographic characteristics of a cohort of 1.1 million Norwegian women. Incidence rate ratios are calculated in Poisson regression analyses of person-years at risk. Our simulations show that the joint analysis in general yields unbiased risk estimates, but the number of cases must be rather high to achieve reliable results. Risk estimates from separate analyses can be seriously biased, although the amount of bias depends on the strength and direction of associations with cancer risk. With a total of 5500 cancer cases, the estimators for age at last birth and time since last birth were 13-78 per cent and 5-66 per cent more efficient in the joint than in the separate analysis, respectively. Significance levels were close to the nominal 5 per cent in the joint analysis, but about twice as high in the separate analysis. Adding an effect of biological infertility on cancer risk among nulliparous women, without taking it into account in the analyses, did not seriously affect risk estimates in the joint model.
A case-control study of multiple sclerosis (MS) has been carried out in western Norway. The study included 93% of the patients who had clinical onset of MS in the county of Hordaland during the years 1976-86 (N = 155) and 200 controls, marginally matched for age, sex and residence. There was no statistically significant difference between MS patients and controls with regard to exposure to organic solvents, exposure to the combination organic solvents and welding or to organic solvents and other chemical compounds.
To examine relations between the risk of epithelial ovarian cancer and time-related effects of pregnancies, we analyzed data from a prospective study of 1,145,076 women in Norway aged 20 to 56 years. The mean follow-up time per woman was 16.4 years and a total of 1,694 women were diagnosed with epithelial ovarian cancer. Incidence rate ratios (IRR) were estimated by Poisson regression analysis of person-years at risk. The risk of epithelial ovarian cancer decreased with an increasing number of full-term pregnancies (IRR = 0.56, 95 percent confidence interval = 0.48-0.67 for three pregnancies cf one). However, no further reduction in risk was seen after the third pregnancy. The association with parity became weaker with increasing age at last birth. Further, the reduction in risk among parous women compared with nulliparous women was more pronounced shortly after birth. Both higher age at last birth and shorter time since last birth were associated with a reduction in risk, although these relations were seen mainly for the first and second births. Increasing age at first birth was associated with a decrease in risk among uniparous women but not among multiparous women. Our results indicate that the relations between the incidence of epithelial ovarian cancer and reproductive factors are more complex than previously believed.
The survival of 1098 patients with ulcer perforation in Norway during the period 1952-1990 was compared with expected survival. Cox regression models incorporating population mortality rates, were used to analyse effects of sex, age, year of birth, and year at risk on excess mortality. Survival was lower in patients than in the general population through a follow-up period of 38 years. Relative survival was lower in women as compared to men, due to more delayed treatment. Long-term survival was lower after praepyloric perforations than after the other perforation types. Relative survival was higher in patients treated 1952-1970 than in those treated more recently. However, adjustment for year of birth revealed a decline in short-term mortality with calendar time, which is in accordance with improved management during the study period. Relative mortality, particularly long-term mortality, was higher in younger birth cohorts, suggesting a shift towards more serious etiologies.