Tor Bjerkedal

Incidence of Sickness Certification: Proposal for use as a health status indicator

Cause-, sex-, and age-specific incidences of sickness certification in a total population are reported. The population at risk of having a sickness certificate issued was 106,019 employed persons 16-69 years of age. The annual incidence of sickness certification was estimated at 580 per 1,000 employed persons per year (females 596, males 568). The most frequent causes of sickness certification, according to diagnostic groups, were diseases of the respiratory system, musculoskeletal/connective tissue diseases, mental disorders, and injuries. Adjusted for age, injuries were found to be less frequent causes of sickness certification among females than males (p less than 0.001), while the reverse was true for mental disorders (p less than 0.01). Among single diagnoses, other nonarticular rheumatism (including myalgia) was more frequent among females than males, while the opposite was true for backpain without radiating symptoms (p less than 0.001). Comparisons with morbidity studies indicate that diagnoses stated on initial certificates, issued to employed persons in the total population, give a reflection of a populations health problems. This suggests that sickness certification may provide a basis for a health status indicator which may prove useful in planning and evaluation of occupational health, general practice, and community health.

The association of parity and birth weight: testing the sensitization hypothesis

The increase in birth weight with parity was studied in sibships of 2, 3, and 4 children using large samples from the Norwegian Birth Registry. Families with full sibs were compared to families with maternal half-sibs. The sensitization hypothesis of Warburton and Naylor predicts no increase in birth weight with parity when the mother changes mate. The hypothesis was not supported by the data, since similar increases in birth weight with parity were found in both types of families. A small effect of the sex of the first child on the birth weight of the later born children was observed.

Small-for-gestational age births in successive pregnancy outcomes: results from a longitudinal study of births in Norway

In this population-based study, a strong tendency to repeat small-for-gestational age (SGA) deliveries in successive births has been documented. Mothers who showed this tendency (repeater mothers) differed from mothers who had only one SGA delivery in their first three single births. In the group of mothers with only one SGA birth, there was an association between the SGA birth and such pregnancy complications as preeclampsia, vaginal bleeding, and placental pathologies. No similar association with medical complications during pregnancy was found for the repeater mothers. Instead, these mothers were characterized by lower educational attainment and lower socio-economic status based on husbands occupational groupings. Thus, the tendency to repeat SGA birth appears to be mediated in part through more adverse living conditions and lifestyle habits.

Epidemiology of sickness certification--a methodological approach based on a study from Buskerud County in Norway.

This paper is part of a broader study of doctors “sickness certification” practice, which is correlated with, but not the same as, “sickness absence” or “sickness benefits”. In order to obtain a total picture, information on sickness certification must be related to the population at risk, i.e. the epidemiology of sickness certification in a total population defined geographically. There is no routine registration system that provides statistics of sickness certification in Norway. Neither is there current information about those of the population who at any one time are entitled to sickness benefits, i.e. the population at risk. The aim of the present paper is to discuss the problems of estimating annual incidences of sickness certification, and to describe the results according to patients sex, age, and place of residence. The study is based on all “initial certificates” received at the National Insurance Offices in Buskerud county during a period of four weeks in 1985. The population at risk was estimated at 106019 employed persons aged 16-69 years, and the annual incidence of sickness certification at 580 per 1000 employed persons per year (females 596, males 568). The highest incidence was found in the age group 20-29 years (females 739, males 741). In the age groups 30-39 and 40-49 years, incidences were significantly higher in females than males. The standardized incidence ratio was significantly lower than average for both females and males in agricultural municipalities, while it was significantly higher than average for females 30-39 years old in urban municipalities. The basis of epidemiological studies of sickness certification used in health services planning and in community medicine is in need of improvement. This challenge is being addressed by the National Insurance Administration in association with the Central Bureau of Statistics in Norway.

The 24-hour rhythmicity of birth. A populational study.

Abstract. The incidence of birth has been determined for each hour of the day for all births in Norway in 1968–1977 of fetuses of 16 weeks of gestation or older, with resident mothers. The 24‐hour incidence variations of births (A) with spontaneous onset and parturition, (B) with spontaneous onset, but delivery intervention, (C) with induced onset, but spontaneous birth, and (D) with induced onset and delivery intervention, are all different.

No significant difference in birth weight for offspring of birth weight discordant monozygotic female twins

Birth weights of offspring of 105 female, monozygotic twin pairs discordant in birth weight were studied. No significant differences were found when offspring of the larger twin were compared with offspring of the smaller twin. The results do not support the hypothesis that in utero effects on females associated with low birth weight will influence their subsequent chance of having low birth weight offspring.

Educational attainment of Norwegian men: influence of parental and early individual characteristics.

The life course perspective in social inequalities in health research has resulted in an increased interest in status attainment processes. Adult status is commonly measured as occupational class, income level or educational attainment, and the latter was applied in this study. The study objective was to estimate the relative contribution of parental and early individual characteristics on educational attainment. The study population comprised all males born in Norway in 1967-1971, and alive at age 28 years (n=160,914). Data on social and biological variables were compiled from birth onwards in several national registers. Information on educational attainment at age 28 years was derived from Statistics Norway. Mean years of education was 12.62 years (SD 2.24). Educational attainment was strongly associated with general ability score at age 18 years and parental educational attainment. Parental income had more limited influence; all other early factors had only marginal effect. Path analysis results suggest that the direct effect of general ability was of the same size as the combined direct and indirect effect of parental education and income. The results suggest that status attainment in this young male population is mainly dependent on general ability and parental education level.

The Heritability of Smoking Behaviour in Pregnancy, and the Birth Weights of Offspring of Smoking-discordant Twins:

Questionnaire information on smoking habits in pregnancy was collated in 341 monozygotic (MZ) and 321 dizygotic (DZ) female twin pair cases from a population-based Norwegian Twin Panel. In a multifactorial model, the intra-pair correlation in smoking was 0.797 (±0.042) in monozygotic (MZ) and 0.443 (±0.075) in dizygotic (DZ) twin pairs, indicating a substantial genetic influence on liability to smoke in pregnancy. The questionnaire information was linked with birth records in the Medical Birth Registry of Norway, and birth weights of offspring of 62 MZ and 100 DZ smoking-discordant twin pairs were studied. Offspring of smoking MZ twins weighed 127 g less than birth order matched offspring of the non-smoking co-twins. This finding is additional evidence that smoking is a direct cause of reduced birth weight in offspring.

Fatal road traffic injuries at age 16–20 years among 611 654 persons born in Norway 1967–1976: multilevel cohort study

Background Road traffic injury is a major cause of death in adolescence. The study objective was to investigate influences of individual and area factors on fatal injuries among motor vehicle occupants, 16–20 years old. Methods All persons born in 1967–1976 in Norway were followed up in several national registries. Associations were analysed in multilevel Poisson regression. Results Road traffic deaths (N=676) constituted a major cause of death, 621 (rate 20.4 per 100 000) were motor vehicle occupants. Boys had higher mortality than girls (adjusted rate ratio (RR) 3.34, 95% CI 2.79 to 4.01). Risk patterns of motor vehicle occupant deaths after non-collision crashes due to loss of control on the road (N=316) and collision crashes showed distinctive differences. Most striking was a strong gradient according to parental education level for boys in the non-collision category (adjusted population preventive fraction 0.83, CI 0.48 to 0.95). A similar gradient was not evident for girls or for collision crashes. Non-collision deaths were associated with residence in less central municipalities (RR 1.61, CI 1.17 to 2.20). Collision deaths were negatively associated with degree of municipal road illumination (RR of 1SD increase 0.66, CI 0.54 to 0.81). Conclusions High mortality among male occupants and the strong socioeconomic gradient in non-collision crashes are alarming. High risk prevention strategies are worth considering. Municipal characteristics of concern were identified but had modest independent impact.