Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Cohort Effect”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 recordsLinked to original sources
PubMed1991

Increasing trend in type 1 (insulin-dependent) diabetes mellitus in childhood in Finland. Analysis of age, calendar time and birth cohort effects during 1965 to 1984.

The Central Drug Registry in Finland ascertained 5,920 incident cases of Type 1 (insulin-dependent) diabetes mellitus diagnosed under the age of 15 years, during 1965-1984. The incidence was higher for males 29.2/100,000 (95% confidence intervals 28.2-30.2/100,000) than for females 26.1/100,000 (25.1-27.1/100,000). A non-linear increase in incidence with age was confirmed, with peaks at ages 2, 9 and 14 years in males and at 3, 5-6 and 11 years in females. A significant temporal variation in incidence was found, adjusting for age and sex. During 1965 to 1984 the incidence rose by about 57% or by 2.4% annually. However, a non-linear curve with two incidence peaks in 1978 and 1983 would better describe the temporal pattern than a linear trend. There was no significant difference in the temporal variation between males and females. The changes in diabetes risk appeared to affect proportionally all age groups under 15 years. Two possible mechanisms were explored: a calendar period effect vs a birth cohort effect. The calendar time period effect was significant alone and also when adjusted for the birth cohort effect. One the contrary, the birth cohort effect was not significant, when adjusted for the calendar period effect. In conclusion, over the past two decades, the incidence of childhood Type 1 diabetes in Finland has increased by about 57%. The pattern of change was a steady rising background incidence superimposed by sudden outbreaks suggesting environmental causative factors.

Adolescent↗
PubMedDate not supplied

[Analysis of the cohort effect on the trend in mortality from motor neuron disease in Spain, 19551-1002].

BACKGROUND: An increase in the mortality due to motor neuron disease (MND) has been reported in Spain over the past 30-40 years. It has been suggested that this increase is due to the cohort effect, but his hypothesis has not been proven. METHODS: The motor neuron disease (MND) mortality statistics by age and by gender were furnished from the Spanish National Institute of Statistics. The mortality specifically by age and the adjusted age-related rates were calculated. By Poisson regression, the cohort effect of birth on the mortality by ages has been analyzed, the cohort effect also having been analyzed by graphic methods. RESULTS: The mortality adjusted by age was declining up until 1969, as of which time it has been on the rise. Each five-year birth cohort increases the risk of dying from MND by 8.5%. CONCLUSIONS: The increase in the mortality due to MND in Spain is the result of a cohort effect.

Adult↗
PubMed1997

Asthma mortality in Australia 1920-94: age, period, and cohort effects.

STUDY OBJECTIVE: To investigate asthma mortality during 1920-94 in Australia in order to assess the relative role of period and birth cohort effects. DESIGN: Asthma mortality (both sexes) was age standardised and examined for changes over time. The data were also examined for age, period, and cohort (APC) effects using Poisson regression modelling. SETTING: National Australian mortality data. PARTICIPANTS: Population (both sexes) aged 15-34 years, 1920-94. MAIN RESULTS: Age adjusted period rates indicate an increase in asthma mortality during the 1950's, and increases and subsequent falls (epidemics) during the mid 1960s and late 1980s. APC modelling suggested an increasing cohort effect (adjusted for both age and period) from the birth cohort 1950-54 onwards. Period effects (adjusted for age and cohort) are characterized by an increase in the 1950s (possibly due to changes in diagnostic labelling), minimal or no increases in the mid 1960s and late 1980s (where period peaks had been noted when data were adjusted for age only), and declines in mortality risk subsequent to the periods where age-period analysis had noted increases. Thus, in Australia, some of the mid 1960s epidemic in asthma deaths, and all of the late 1980s mortality increase, seem to be attributable to cohort effects. CONCLUSIONS: The increase in asthma mortality cohort effect is consistent with empirical evidence of recent increases in prevalence (and presumably incidence) of asthma in Australia, and suggests the need for more research into the underlying environmental aetiology of this condition.

Adolescent↗
PubMed1997

Trends in stroke mortality in Greater London and south east England--evidence for a cohort effect?

OBJECTIVE AND SETTING: To examine time trends in stroke mortality in Greater London compared with the surrounding South East Region of England. DESIGN: Age-cohort analysis based on routine mortality data. SUBJECTS: Resident population aged 45 years or more. MAIN OUTCOME MEASURE: Age specific stroke mortality rates, 1951-92. MAIN RESULTS: In 1951, stroke mortality was lower in Greater London than the surrounding South East Region in all age bands over 45. It has been declining in both areas but the rate of decline has been significantly slower in Greater London (p < 0.0001). The differences in rates of decline were such that stroke mortality is now higher in Greater London for people under 75. The crossover of age specific stroke mortality rates occurred at different periods in different age bands and is consistent with a cohort effect, with similar rates in Greater London and the surrounding south east for men and women born around 1916-21. This cohort effect does not appear to be consistent with past maternal and neonatal mortality rates in these areas, nor, within the limitations of the data, with the ethnic composition of cohorts. CONCLUSIONS: There seems to be a cohort effect on stroke mortality which is not explained by past maternal and neonatal mortality. If the decline in stroke mortality continues at its current rate, the Health of the Nation stroke target is unlikely to be achieved in Greater London.

Age Distribution↗
PubMed1997

Analysis of cohort effects in mixed longitudinal data sets.

Mixed longitudinal designs are among the most efficient for the study of growth and developmental processes. In this approach, one studies several (birth) cohorts, each for a relatively short length of time, and then links the growth curves for the individual cohorts together to obtain the growth curve for the entire length of time spanned by the ages of the subjects in all cohorts. Thus, e.g., in the Nijmegen Growth Study, three cohorts were each studied for 5 years, the intent being to join the three curves together to form a single curve covering the entire period from 4 to 14 years of age. In order for this approach to be valid, there either should be no cohort effects (secular trends) or the fitted curve must be adjusted in some way to correct for such effects if they exist. The question thus arises as to how one should test for the presence of cohort effects and what one should do about them if found. The problems which may arise using height and weight data from the Nijmegen Growth Study are illustrated. In particular for girls, height and weight both show cohort effects (at 9.25 years of age) when the raw data are used. If, however, the observed data are used to estimate the values at the target age, and these values are used in the comparison, differences between the cohorts are no longer significant. The problems are further illustrated using data from a mixed longitudinal data set of cleft lip and palate patients and data from the National Dutch Growth Study 1980.

Child↗
PubMedDate not supplied

Age, period, and cohort effects in marijuana and alcohol incidence: United States females and males, 1961-1990.

Using multiple classification models applied to self-report data on initiation of drug use from nine National Household Surveys on Drug Abuse conducted between 1982 and 1995, this paper shows that the directions of change in period and cohort effects were similar for marijuana and alcohol and for males and females. Period effects--indicative and societal tolerance or support for drug use during 5-year periods between 1961 and 1990--declined between the early 1970s and late 1980s, while cohort effects--indicative of early experiences of birth cohorts favoring drug use--increased. One interpretation is that trends in incidence were determined by two opposing vectors of social forces: Beginning in the 1970s, changes in social policies, values, and drug markets--as reflected in period effects--increasingly acted to reduce incidence, while changes in conditions of childhood socialization--as reflected in cohort effects--increasingly facilitated or encouraged incidence. Especially for marijuana, the increase in cohort effects is larger among females, which gives rise to gender convergence--approximately equal male and female incidence rates for both drugs--by the late 1980s. An innovative method of the paper is the adjustment of incidence rates for reporting bias.

Age Distribution↗
PubMed2001

Evidence of a cohort effect for age at onset of schizophrenia.

OBJECTIVE: The authors address whether a possible age-at-onset cohort effect may have introduced a bias into anticipation studies of schizophrenia. METHOD: A retrospective review of the medical records of all admissions for psychotic disorders (N=877) was conducted. All subjects with a confirmed DSM-IV diagnosis of schizophrenia and age-at-onset data were included (N=419). For analyses, subjects were placed into one of three successive birth cohorts: 1905-1944 (N=96), 1945-1964 (N=200), and 1965-1984 (N=123). RESULTS: The mean age at first appearance of psychotic symptoms and, similarly, the mean age at first hospitalization significantly decreased over time in successive birth cohorts (25.3, 23.3, and 20.4 years, respectively, for age at first appearance of psychotic symptoms). CONCLUSIONS: This potential birth cohort effect for age at onset of schizophrenia needs to be incorporated into genetic models.

Adult↗
PubMed1997

Age, time, and cohort effects on functional status and self-rated health in elderly men.

OBJECTIVES: This study investigated age-related changes in functional status and self-rated health in elderly men, taking into account changes over time and differences between birth cohorts. METHODS: The Zutphen Elderly Study is a longitudinal study of men born in the Netherlands between 1900 and 1920. Functional status and self-rated health were measured in 513 men in 1990, in 381 men in 1993, and in 340 men in 1995. Age, time, and cohort effects were analyzed in a mixed longitudinal model. RESULTS: Longitudinal analyses showed that during 5 years of follow-up, the proportion of men without disabilities decreased from 53% to 39%, whereas the percentage who rated themselves as healthy decreased from 50% to 35%. Cross-sectional analyses confirmed changes in functional status, suggesting an age effect. Time-series analyses confirmed changes in self-rated health, suggesting a time effect. No birth-cohort effects were found. CONCLUSIONS: Functional status deteriorates with age, whereas self-rated health is not related to age in men aged 70 years and older. The observed 5-year decline in self-rated health seemed to be due to a secular trend.

Activities of Daily Living↗
PubMed1988

Age and recognition of depression: implications for a cohort effect in major depression.

Studies relying on subjects' retrospective reports have recently been interpreted as indicating that individuals born since World War II are at increased risk for a diagnosis of lifetime major depression. Examining the validity of this 'cohort effect' is essential, given the potential importance of such a phenomenon for research and policy. Among a number of artefactual explanations for the cohort effect is the possibility that older individuals are less likely to recognize depression as a mental disorder, and hence are less likely to remember depressive episodes as such, or to report these episodes in interviews on mental health. To test whether age was related to the recognition of major depression as a mental problem, we analysed responses from 152 randomly selected community residents on whether a vignette describing DSM-III major depression represented a psychological or emotional problem. Older respondents were much less likely to characterize major depression this way, even controlling for other factors. Such an age effect may provide a partial explanation for the apparent cohort effect, although the issue is complex and further research is needed.

Adult↗
PubMed1999

Interpreting age, period and cohort effects in plasma lipids and serum insulin using repeated measures regression analysis: the CARDIA Study.

Observed changes in health-related behaviours and disease risk factors may arise from physiological or environmental changes, or from biases due to sampling or measurement errors. We illustrate problems in the interpretation of such changes with longitudinal data from the Coronary Artery Risk Development in Young Adults (CARDIA) study. Mean plasma cholesterol was 14 mg/dl higher in 27- than in 20-year-old black men cross-sectionally, but longitudinally it declined by 4 mg/dl during the 7 years. To sort out these contradictory assessments of the effect of age/passage of time, we estimated age and period effects under the assumptions that age effects are a smooth function of age independent of period, and that period effects are changes common to persons across all ages. Simple estimates the age effect, such as the cross-sectional age slopes, may be confounded by cohort effects, by interactions of time and age after baseline, or by the occurrence of non-linearities in response after baseline. We note examples of each potential type of bias. The data and background literature support the assumption that cohort effects do not seriously compromise interpretation for these variables in the CARDIA study. Strong secular decreases in plasma cholesterol, apparently due to population-wide dietary change, mask increases with ageing. Age increases in triglycerides are largely explained by increases in body fatness. For these data, we cautiously accept the cross-sectional age slope as an estimate of ageing and the age-matched time trend as an estimate of secular trend.

Adolescent↗
PubMed1994

Increasing prevalence of Helicobacter pylori infection with age: continuous risk of infection in adults rather than cohort effect.

It remains unclear whether acquisition of Helicobacter pylori is due to a continuous risk of acquiring the infection or a cohort effect. In this prospective 3-year cohort study, the seroprevalence, conversion, and reversion of H. pylori infection as determined by IgG antibodies was examined. The cohort consisted of 316 randomly selected, nonpatient subjects aged 18-72 years who each provided at least 2 suitable samples. Seroprevalence of H. pylori increased from 21% in the third decade to 50% in the eighth decade. Crude annual seroconversion rate was 1% and the "spontaneous" seroreversion rate was 1.6%. Age was the only identified risk factor for H. pylori infection. A continuous risk of acquisition of 1%/year rather than a cohort effect best explains the pattern of H. pylori infection in this Canadian population. Seroconversion continues in adult life, and spontaneous reversions do occur, especially in the later decades.

Adult↗
PubMed1989

Decline of height with age in adults in a general population sample: estimating maximum height and distinguishing birth cohort effects from actual loss of stature with aging.

The decline in stature with age among adults is well documented. Although part of this represents a birth cohort effect, actual height declines among older individuals are known to contribute to the effect. In this study we used longitudinal changes in the heights of adults in a general population sample to determine the rate of decline in height over time in individuals of different ages. This allowed an estimation of the age at which decline in height begins, a value close to age 40 in both sexes. It also allowed derivation of equations from which the maximum height of subjects can be estimated on the basis of their sex, current height, and age. These equations should prove useful when examining the effect of aging per se on physiological measurements that are height dependent. The data also allow one to compare the magnitude of the effect of year of birth with that of the actual decline in height seen among the elderly. We estimate that approximately 60% of the smaller stature of older male subjects and 45% of the smaller stature of older female subjects is a birth cohort effect deriving from the secular trend toward greater stature; the remainder is a result of an actual decrement in height after the age of 40.

Adult↗
PubMed1984

Period, age, and cohort effects on substance use among American youth, 1976-82.

Period, age, and cohort effects on substance use are differentiated for American youth 18 to 24 years old during the period from 1976 to 1982. The data are provided by the Monitoring the Future project, an ongoing study which employs a cohort-sequential design. Weighted least squares regression is used to find plausible and parsimonious models to account for the observed variation in 12 different classes of drugs, both licit and illicit. The point is made that there are no definitive ways to differentiate among the types of effects; thus, any interpretation is open to debate. Period effects involving increased use occurred for cocaine, amphetamines, and methaqualone, while decreases occurred for barbiturates, tranquilizers, and psychedelics other than LSD. Marijuana showed a curvilinear period effect, first increasing then decreasing. Effects of age were more complex. There were increases in the year after high school for daily cigarette use, but not for monthly use. Monthly and daily alcohol use increased with age. A measure of heavy drinking showed a curvilinear trend, first increasing and then decreasing. Annual use of cocaine showed an increase between the ages of 18 and 21. Annual use of narcotics other than heroin showed a linear age decrease. Clear class (or cohort) effects appeared for cigarette use, with each successive class smoking less.

Adolescent↗
PubMed1991

Sex-specific trends in mortality for the aging population in Norway: a model with age, period, and cohort effects.

During the last few decades, the citizens of most western countries have experienced an increased expectation of life. The rate of this change differs for males and females. We evaluated reasons for this pattern, using a Poisson model, with age, period, and cohort effects applied to vital statistics data from the Central Bureau of Statistics of Norway. The data comprised the total Norwegian population aged 45 to 104 years who died in the period from 1966 until 1986. Differential changes in life expectancy for the elderly are explained by differences in sex-specific cohort effects. We also observed an extra-Poisson variation, or overdispersion, in the distribution for females.

Age Factors↗
PubMed1987

The changing relationship between age and suicide rates: cohort effect, period effect or both?

Massive changes in suicide rates over time have been recognized in the United States. An attempt has been made to describe these changes with age-period-cohort analyses. A variety of approaches has led us to conclude that suicide rates of non-white males, white and non-white females can be described adequately without a cohort effect. Recent suicide trends lead to the conclusion that a model based on a rising rate in more recently born white male cohorts coupled with an independent age effect could be rejected. If a cohort effect is postulated for more recent birth cohorts, it would require that the cohort suicide rate is decreasing with each successive birth cohort. Models based on high suicide rates in recent cohorts and additive age effects are probably misleading for future predictions. An association was noted between recent changes in the teenage and young adult suicide rates and rates of depression. Both may be the product of similar social influences.

Adolescent↗
PubMed1997

Helicobacter pylori and the birth cohort effect: evidence of a continuous decrease of infection rates in childhood.

OBJECTIVE: To investigate whether the decrease in rate of Helicobacter pylori infection in subsequent birth cohorts has continued during the last decades. METHODS: Determination by ELISA of IgG H. pylori antibodies in 314 serum samples from Dutch children (age 6-8 yr, n = 154) and young adolescents (age 12-15 yr, n = 160), collected in 1978 and 1993. RESULTS: The prevalence of H. pylori declined from 19% to 9% at age 6-8 yr and from 23% to 11% at age 12-15 yr. For the whole study population, a decline from 21% to 10% (p = 0.01) was observed between 1978 and 1993. On the basis of these data and an incidence of infection with H. pylori of 0.3% per year during the same period, a model for both past and future prevalence rates of H. pylori in the Dutch population was calculated. The outcome demonstrates a decrease from more than 50% around World War II to less than 20% for the whole population around year 2040. CONCLUSIONS: H. pylori infection rates in childhood have continued to decline until recent decades, demonstrating a persistent birth cohort effect. This decline will result in a very low prevalence of H. pylori infection in the Dutch population during the next decades, becoming even lower as the observed decline in children and young adolescents continues.

Adolescent↗
PubMed2000

Age-related decreases in the prevalence of myopia: longitudinal change or cohort effect?

PURPOSE: The prevalence of myopia shows a decline with age in cross-sectional studies. This pattern may represent an increase in the prevalence of myopia in younger generations, possibly through increased exposure to near work, or an intrinsic age-related decline in myopia prevalence. Data were analyzed from published studies to determine which of these two alternatives better explains the data: a cohort effect of changing prevalence by decade or a longitudinal effect of changing prevalence as a function of age. METHODS: Prevalence data were taken from three studies conducted in the late 1980s and compared with those obtained indirectly from a national survey conducted in the early 1970s. The prevalence of myopia was then plotted as a function of age and year of birth. RESULTS: The pattern of change in the prevalence of myopia as a function of age was consistent across all studies when data were scaled relative to the prevalence of myopia at age-range midpoints from 44.5 to 49.5 years. The pattern of change was not consistent as a function of year of birth. When the data were scaled relative to the prevalence of myopia among those with years of birth from 1940 to 1942 and plotted by year of birth, results from the early 1970s were offset from those of later studies by approximately 18 years. CONCLUSIONS: The decline in the prevalence of myopia in older adults between the early 1970s and the late 1980s can be better explained by age than by year of birth. The prevalence of myopia appears to decrease because of an intrinsic age-related decrease in the amount of an individual's myopia rather than because of a cohort effect of increasing prevalence over time. The hypothesis that increasing environmental exposures to near work in recent decades have changed the prevalence of myopia is not supported by this analysis.

Adolescent↗
PubMed1988

Period, age, and cohort effects on substance use among young Americans: a decade of change, 1976-86.

In an earlier article in this Journal, we reported analyses that differentiated among period, age, and cohort effects on substance use among American youth 18 to 24 years old, from the high school classes of 1976 to 1982 during the period of 1976 to 1982. The present analyses extend the classes and years to 1986, and the age range to 18-28. A cohort-sequential design is employed, based on annual surveys of nationally representative samples of high school seniors, plus annual follow-up surveys of each senior class. Twelve different classes of drugs, both licit and illicit, are examined. Several different types of period, age, and cohort effects over the last decade are identified. Alcohol use (monthly and occasions of heavy use), and the use of marijuana, cocaine, amphetamines, methaqualone, barbiturates, LSD, psychedelics other than LSD, and tranquilizers all showed period effects. Occasions of heavy drinking, cigarette smoking, monthly and daily use of alcohol, and annual prevalence of cocaine, amphetamines, barbiturates, LSD, and narcotics other than heroin showed age effects. Class effects were seen for cigarette smoking and daily marijuana use.

Adolescent↗