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PubMedDate not supplied

Cohort effects in a genetically determined trait: eye colour among US whites.

BACKGROUND: While the inheritance of eye colour is likely polygenic, blue eye colour is thought to follow an inheritance pattern similar to that of a recessive trait. Consequently, age-related differences in the prevalence of blue eye colour would be unanticipated. AIM: This study explores the finding and explanation for birth cohort differences in the prevalence of blue eye colour in the US white population. SUBJECTS AND METHODS: Data from the first (1971-1975) and third (1988-1994) US National Health and Nutrition Examination Surveys (NHANES-I and NHANES-III), nationally representative surveys of the US population, were analysed. Trends in eye colour prevalence by birth cohort were analysed together with mortality rates according to eye colour. US census data (1980) were examined to explore cohort differences in ancestry and assortative mating by ancestry. RESULTS: The prevalence of blue eye colour among non-Hispanic whites in NHANES-III was 57.4% (95% CI: 50.1-64.7) for individuals born between 1899 and 1905 compared to 33.8% (95% CI: 31.3-36.5) for those born between 1936 and 1951. No association was found between survival and eye colour, nor was a cohort effect evident for primary ancestry. However, proportions reporting only one ancestry in census data declined with successive birth cohorts. CONCLUSIONS: A cohort effect in blue eye colour prevalence was found for the US white population. A secular trend of decreasing assortative mating by ancestry is the likely explanation.

Adult↗
PubMed2000

Dental service rates: age, period, and cohort effects.

OBJECTIVE: Variation in dental service provision over time has been related to changes in factors such as oral health and demographics. Dentist factors such as age and cohort effects are also potential sources of influence. The aim of the study was to examine the operation of age, period, and cohort factors on variation in service rates. BASIC RESEARCH DESIGN: data were collected by a mailed survey of a random sample of 10% of male and 40% of female dentists from each state/territory of Australia in 1983-84, 1988-89. and 1993-94 with response rates of 73, 75 and 74% respectively. MAIN OUTCOME MEASURES: Data on main areas of service were obtained from a log of service items provided on a typical day. RESULTS: Poisson regressions of rates for the 10 main areas of service over time showed increased rates over the study period for diagnostic, preventive, endodontic, crown and bridge, general/miscellaneous and orthodontic services, and decreased rates of prosthodontic services. Goodness-of-fit tests indicated that models for periodontal and endodontic services had a good fit. However, only endodontic services were readily interpretable in terms of descriptive trends. While the age-period-cohort model was preferred, age-period and age-cohort models were also examined because of problems of identification with age-period-cohort models. Endodontic rates were higher among younger dentist birth cohorts, and increased over the 10-year study period for most cohorts of dentists. CONCLUSIONS: If these effects for dentist cohorts were extrapolated over the next 10-year interval, the distribution of services would alter, with endodontic services emerging as a dominant area behind restorative, diagnostic, and preventive services.

Adult↗
PubMed1985

Primary malignant nervous system neoplasms. Birth cohort effect in the elderly.

Current data indicate that mortality for primary malignant nervous system neoplasms (NSNs) provides a fairly accurate index of incidence. Average annual age- and sex-specific death rates among whites for primary malignant NSNs in the 48 contiguous United States from 1940 through 1975 showed a marked cohort effect among the elderly of either sex. For white men aged 60 through 64 years, mortality increased steadily from 5.3 per 100,000 per year for those born in 1880 to 16.1 per 100,000 per year for the 1910 cohort. No definite cohort effect was seen in the young. The increase in mortality could be due to better diagnosis and more complete case ascertainment for deaths due to primary malignant NSNs, but further studies are required to distinguish a real from an artifactual increase in mortality.

Age Factors↗
PubMed1993

The cohort effect and Helicobacter pylori.

A total of 631 serum samples collected in 1969, 1979, and 1989 from adults and children were screened for Helicobacter pylori by Western blot analysis. Results showed that H. pylori seroprevalence has become less frequent over the 20-year period. By studying seropositivity by year of birth, the magnitude of a cohort effect of H. pylori seropositivity was estimated. The odds of being seropositive decreased by 26% per decade, P = .008 (95% confidence interval, 8%-41%). Estimates of seroprevalence adjusted for both age-specific variation and the cohort effect suggest that most seropositivity in adults occurs by the age of 15 years. The implication of these findings is that H. pylori infection is becoming less frequent and is predominantly acquired in childhood.

Adolescent↗
PubMedDate not supplied

The development of self-rated health during adolescence: an exploration of inter- and intra-cohort effects.

Self-rated health is a commonly used measure of physical health status. While the development of one's perception of self-rated health likely occurs during childhood and adolescence, its development has been largely unexplored. This study addresses this issue by examining the relationship between adolescent self-rated health and personal (sex, age) and situation (family structure, family income) factors at five different time intervals to identify inter- and intra-cohort effects as well as concomitant changes in adolescent health compromising behaviour, specifically substance use. Five waves between 1989 and 1997 of the biennial Ontario Student Drug Use Survey (OSDUS) by the Addiction Research Foundation (ARF) consisting of 19,512 cases were examined. The results indicate the presence of both inter- and intra-cohort effects on self-rated health. In addition, health-compromising behaviours had a varied effect on self-rated health across grade. This analysis confirms some previous findings but also presents contradictory evidence by identifying the complexity of relationships among these factors and self-rated health.

Adolescent↗
PubMed1997

Time trend and age-period-cohort effects on gastric cancer incidence in Zaragoza and Navarre, Spain.

STUDY OBJECTIVE: To describe time trends in gastric cancer incidence in Zaragoza and Navarre, and to investigate time period and birth cohort as determinants of such trends. DESIGN: Cases from two registries were grouped into five year intervals and the following were calculated: age specific and sex specific incidence rates, and the male to female ratio. Log linear models including age, period of diagnosis, and birth cohort were fitted. SETTING: The Zaragoza Cancer Registry covers the province of Zaragoza, which has a population of 824,776 (403,755 men and 421,021 women). The Navarre Cancer Registry covers the province of Navarre which has 512,512 inhabitants (254,786 men and 257,726 women). In both cases population figures were based on the late census. PATIENTS: These comprised incident cases of gastric cancer reported to the Zaragoza Cancer Registry in 1963-87 and to the Navarre Cancer Registry in 1973-87. MAIN RESULTS: Navarre registered higher adjusted and cumulative rates than Zaragoza for both sexes. In both provinces, there were relative declines in the rates for men and women of 3% and 4% respectively per year. In Zaragoza, the risk of developing stomach cancer fell in generations born between 1888 and 1933, and rose in subsequent birth cohorts in both sexes, while in Navarre the cohort effect showed an approximately linear risk for both sexes. Both provinces recorded increases in risk associated with cohorts born between 1933 and 1943. CONCLUSION: The incidence rates of gastric cancer fell in both Zaragoza and Navarre. The reason for the greater incidence of gastric cancer in Navarre remains unknown. Trends in rates seem to be mainly linked to birth cohort. Increases in risk in generations born after 1933 may be ascribable to nutritional deficiencies in the early years of life.

Adolescent↗
PubMed2005

Birth cohort effect on lung cancer incidence in Taiwanese women 1981-1998.

Lung cancer has been the main cause of cancer-related mortality in Taiwanese women since 1986. Gradual increases in both awareness of risks and use of extractor fans in kitchens should reduce the incidence of this disease. To investigate the birth cohort effect on lung cancer incidence in Taiwanese women for 1981-1998, an age-period-cohort (APC) model analysis was employed to study the effects of age, time periods, birth cohorts and histological types of lung cancer. A significant increase in lung cancer incidence among women was found for the period 1981-1998 (r=0.96, P<0.05), principally of adenocarcinoma, then squamous cell carcinoma. Age is the strongest predictor according to the APC model. The birth cohort of 1917-1926 has the highest risk of lung cancer. However, in recent cohorts, particularly those born after 1956, the incidence has fallen. The declining incidence in younger cohorts may be due to the increased use of extractor fans in kitchens reducing exposure to carcinogenic fumes from cooking oil.

Adult↗
PubMed1989

Cohort effects in the prevalence of caries in child populations in Tanzania.

In 1984, a four-year mixed-longitudinal study of oral health was begun in Morogoro Town and Morogoro District, Tanzania. Its main goal was to detect a possible upward trend in prevalence of caries in child cohorts in this developing country. The sample consisted of 722 seven- to nine-year-olds in 1984, 833 seven- to 11-year-olds in 1986, and 989 seven- to 13-year-olds in 1988. Mixed-longitudinal studies provide the opportunity for application of the Age-Period-Cohort analysis. On the basis of external information, either age and/or cohort and/or period effects can thus be isolated. Apart from significant age and period effects, a cohort effect was found, indicating that the prevalence of caries has decreased in these child populations between 1984 and 1988.

Adolescent↗
PubMed2002

Cohort effects on gender differences in alcohol dependence.

AIMS: The present study investigated the presence of cohort effects on gender differences in the course, severity and symptomatology of DSM-III-R alcohol dependence in a community-based sample. DESIGN: A comparison of substance-related variables among men and women divided into two groups based on the median birth year of the sample was conducted. PARTICIPANTS: Participants were 468 men and 132 women with life-time alcohol dependence, the vast majority of whom were born between 1941 and 1960. MEASUREMENTS: Substance use and DSM-III-R substance use disorders were assessed by a structured interview administered in person. FINDINGS: Individuals born after 1951 had higher rates of alcohol dependence. Among individuals with alcohol dependence, those born after 1951 had an earlier onset and longer duration of alcohol-related problems. Significant interactions indicated that these effects were stronger for women than men. CONCLUSIONS: Risk for alcohol dependence appears to be rising in younger generations, and particularly for younger women, making them an important target group for prevention and treatment programs.

Adult↗
PubMed1989

Linkage analysis with cohort effects: an application to X-linkage.

The LIPED program has been modified to incorporate cohort effects in a linkage analysis. Very significant positive lod scores are obtained between bipolar affective disorder and both the deutan and protan markers on the X-chromosome. Lod score methods are shown to be sensitive to the specification of the age of onset distributions and the parameters of the model of transmission.

Age Factors↗
PubMed1979

Analysis of cohort effects from cross-sectional data.

A statistical model and computer program are described to analyze data fro the existence of cohort effects. The analysis leads to the separate assessments of cohort, time and age influences on a series of age-specific rates that are available in cross-sectional form. The assessment of these three factors can possibly yield insights into specific disease etiologies.

Age Factors↗
PubMed1993

Time trends, cohort effects, and geographic patterns in stroke mortality--United States.

Trends and patterns in cerebrovascular disease mortality from 1940 to 1991 are examined using provisional and final mortality data from the US National Vital Statistics System. Trends are analyzed in terms of both period and cohort effects. Monthly data are examined using a time series regression model. Geographic patterns use maps ranking state mortality relative to the US average. Final 1989 data indicate that cerebrovascular disease remains the third leading cause of death in the United States, accounting for 145,551 deaths, or 6.8% of deaths from all causes. The age-adjusted death rate from stroke declined one-third during 1979 to 1989, more rapidly than the other ten leading causes of death. Overall, stroke mortality declined steadily from 1950 through the mid-1970s, then accelerated. On a cohort basis, each successive birth cohort since 1890 has improved their life-span experience from stroke deaths. Maps of stroke mortality demonstrate a persistent "stroke belt" in the South over the past decade.

Adult↗
PubMed2003

Lack of ageing cohort effect among sexually acquired HIV infections in Hong Kong.

We studied HIV rate in different age populations and whether there has been on-going new infections in Hong Kong, by examining the age characteristics and their temporal trend of reported HIV infections. It was found that people in the age group 25-34 were worst hit by the local epidemic. Ageing cohort effect was not apparent for the age pattern of sexually-acquired infections reported from 1987 to 2000, with the annual median ages ranged from 31.5 to 36 years (regression coefficient 0.14, 95% confidence interval -0.14 to 0.42, P = 0.295). Similar temporal age patterns were observed for individual subgroups of homo-/bisexuals, heterosexuals and female heterosexuals. The findings suggested the occurrence of new HIV infections over the years in Hong Kong, despite maintenance of a low prevalence. Albeit capturing largely prevalent infections, reported HIV/AIDS data could be tapped for understanding the evolving epidemic pattern to better evaluate and target current prevention programmes.

Adult↗
PubMed2003

Age and birth cohort effects on rates of alcohol dependence.

BACKGROUND: Epidemiological studies of traits such as alcohol dependence and depression have often found lifetime rates in younger individuals exceeding those found in older individuals. This suggests additional influences of birth cohort or period effects so that individuals in later-born cohorts have an increased lifetime risk. METHODS: Data from the Collaborative Study on the Genetics of Alcoholism were used to investigate secular trends for alcoholism and related conditions and to examine risk predictors while taking the cohort effect into account. We used data on 4099 interviewed parents and siblings of alcohol-dependent subjects and 1054 members of control families. We used survival analysis techniques and the Cox proportional hazards regression model to estimate the relative risk for demographic covariates. We used the relative sample to predict risk in the sibling of the proband and family history information to determine whether there was a bias when deceased individuals were excluded from analysis. RESULTS: In the control sample, we observed a 1.8% lifetime rate of DSM-III-R alcohol dependence in women born before 1940, as contrasted to a 13% rate in women born after 1960, and a 15% lifetime rate in men born before 1940, contrasted with a 28% rate in men born after 1960. As expected, lifetime rates in relatives were increased when compared with controls. Highly significant risk ratios (RR) were observed for gender (RR, 2.3), cohort of birth (RR, 1.5 over a decade), daily smoking (RR, 2.0), heavy smoking (RR, 3.0), and comorbid diagnoses of antisocial personality (RR, 2.2) and depression (RR, 1.6). Analysis of the family history data indicated higher rates of alcohol dependence in relatives who were deceased compared to those who were living. CONCLUSIONS: Marked cohort differences were observed and may reflect real changes over time, or artifacts of memory recall, differential mortality, or public awareness. The analysis of all relatives (living or deceased) indicates that associated mortality may, in part, explain the secular trends seen when analyses are restricted to living, personally interviewed individuals.

Adolescent↗
PubMed1989

Blood pressure changes with aging: evidence for a cohort effect.

Data from cross-sectional surveys show an increase in systolic blood pressure with increasing age. However, cross-sectional data can be misleading. Our purpose in this study is to prospectively describe changes in systolic and diastolic blood pressure levels over time in community-dwelling elderly persons. The participants were 1,917 men and women aged 65 to 98 yr who had participated at least seven years in the Florida Geriatric Research Program, a community-based, multi-phasic health screening program located in Dunedin, Florida (USA). Our results show that contrary to the cross-sectional data, systolic and diastolic blood pressure levels tend to decrease with increasing age. Mean systolic blood pressure in women at the baseline visit (Visit 2) was 143 mmHg and three years later (Visit 5) it had dropped to 140 mmHg. This downward trend was consistent at all ages and for both men and women. Stratification by use of antihypertensive medication, weight change, and survivorship did not alter this association. Further follow-up of this cohort to Visit 7 revealed a U-shaped trend of blood pressure with aging. There was also clear evidence of a cohort effect, as the age-specific mean systolic blood pressure was consistently lower in each younger 5 yr birth cohort. Our results suggest that in a healthy elderly population, systolic and/or diastolic blood pressure levels do not increase with aging; this finding may have implications for the diagnosis and treatment of hypertension in the elderly.

Aged↗
PubMed1980

Aging and suicide? maturation or cohort effect?

Within the field of gerontology investigators have been concerned with determining whether social behavior can be explained by a cohort effect or a generational maturation effect. This paper considers the question by examining suicidal behavior from a subjective perspective. A Suicide Potential Scale is constructed for a sample population in the city of Flint, Michigan, and it is shown that the scale fits the Guttman scale criteria. The mean suicide potential scores of various age groups in the sample are then examined and it can be seen that the data lend support to the cohort model with the exception of individuals seventy-five and older, where it appears that maturation factors play an important role in explaining suicidal behavior.

Adolescent↗
PubMed2005

Hepatitis C virus infection in cameroon: A cohort-effect.

A hepatitis C virus (HCV) serological study conducted in 2003 on 1,434 individuals in Yaounde and other HCV seroepidemiological studies on 2,066 sera sampled between 1993 and 1997 in four geographically distinct rural areas (Ntem, Mekas, Yokadouma, and Nditam) in Cameroon, are described. Two patterns of HCV seroprevalence were observed. The first pattern, represented by Nditam and Yokadouma populations, showed low HCV seroprevalence rates (2.9% and 3.3%, respectively) increasing moderately with age (9.0% and 16.7% after age 50). The second pattern showed high seroprevalence rates (6.9% for Yaounde, 14.4% and 16.7% for Ntem and Mekas, respectively). These rates increased dramatically with age (32.8%-49.5% after age 50). The age-specific anti-HCV prevalence curve of the 1993 Mekas survey paralleled those of the 1997 Ntem and 2003 Yaounde surveys. Using the year of birth as the x-axis, the three curves closely matched each other. This clearly indicates a cohort effect for which the seroprevalence trends are clearly related with the year of birth, rather than the age. The highest prevalence was observed among people born around 1940.

Adolescent↗
PubMedDate not supplied

Birth cohort effects underlying the increasing testicular cancer incidence in Canada.

PURPOSE: To examine the pattern of testicular cancer incidence by age, time period and birth cohort since 1969 in Canada. METHODS: In addition to analyses of the secular trends by age group and birth cohort separately, an age-period-cohort model and the submodels with standard Poisson assumptions were fitted to the data. RESULTS: The overall age-adjusted incidence of testicular cancer increased in Canada, from 2.8 per 100,000 males in 1969-71 to 4.2 in 1991-93. The younger age groups showed much higher absolute incidence rates in the recent period compared with those in the early period. Age-period-cohort modelling of data restricted to males aged 20-84 years suggested that the observed increase in testicular cancer could be largely attributed to a birth cohort effect. A steady increase in risk was observed among men born since 1945; those born between 1959 and 1968 were 2.0 (95% CI, 1.5-2.6) times as likely to develop testicular cancer as those born between 1904 and 1913. CONCLUSION: The risk of testicular cancer has increased over time and changing exposure to environmental factors early in life may be responsible for this.

Adolescent↗