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PubMed1994

Diminished recall and the cohort effect of major depression: a simulation study.

Several large-scale epidemiological surveys have reported increasing lifetime rates of psychopathology among recently born cohorts. In the case of Major Depressive Disorder (MDD) younger cohorts tend to manifest higher lifetime prevalences of the condition than older cohorts, at any given age. In some studies, cohort differences are so large that the youngest cohort exceeds the lifetime prevalence of the oldest cohort well before passing through their total period of risk. The data on lifetime prevalences that support the existence of secular differences, however, has typically been collected in cross-sectional studies. Thus, individuals are interviewed at a single point in time and asked to recall all prior psychopathology. Due to poor recall, this design may greatly underestimate earlier experiences. In fact, cohort differences are not limited to MDD; similar results have been reported for a wide range of psychopathology, suggesting methodological problems at data collection. We have conducted a simulation study to examine the magnitude of annual rates of forgetting that could produce the secular trends reported for MDD. Small, but constant annual rates produce striking, 'cohort effect-like' curves. The rates needed to reconstruct the reported effect are compatible with published values for test-retest studies of lifetime recall of MDD. This simulation study does not rule out the existence of a cohort effect in some psychiatric disorders, but stresses the possible limitations of using cross-sectional studies to investigate secular trends.

Adolescent↗
PubMed1997

Gastric cancer in the European Union (1968-1992): mortality trends and cohort effect.

PURPOSE: To analyze patterns and trends in gastric cancer mortality in the European Union (EU) over the period 1968-1992, paying special attention to changes associated with birth cohort. METHODS: Poisson log-linear models were used to quantify geographic differences and relative annual changes. To assess trends associated with birth cohort, invariant parameters from sex-specific age-period-chohort models (net drift and curvature), for each country, were used to choose a restricted slope range for cohort effect. RESULTS: Gastric cancer mortality declined throughout the EU. The male-to-female ratio stood at around 2 in all countries, yet showed a slight rise over time. Portugal reported the highest age-adjusted rates for men and women (45.63 and 23.31 per 100,000 person-years, respectively). The rate ratio between two extreme countries (Portugal/Denmark) exceeded 3. Quantitative intercountry differences were found in trend slopes, with a decrease of 5% per annum in Finland. Risk of dying associated with birth cohort decreased over successive generations. Small local rises in risk, in almost all countries among generations born around the 1940s, support the importance of diet early in life in the etiology of gastric cancer. CONCLUSIONS: Despite the substantial decline in gastric cancer mortality witnessed in the EU, stress must be accounted for the wide differences among countries and the smaller decline in the youngest generations, particularly among women. This latter finding suggests a possible stabilization or even a rise in the rates in future, rendering it important for these trends to be monitored over the next few years.

Adult↗
PubMed1995

The increase of Parkinson's disease mortality could be due to a cohort effect.

INTRODUCTION: An increase of Parkinson's disease (PD) mortality has been observed in various countries during the last 3 decades. An analysis was done in order to define whether this trend could be due to a cohort effect. MATERIAL & METHODS: The mortality from PD in Italy during the period 1963-1987 was analyzed by means of a simplified cohort method. A mortality rate ratio (MRR) was also calculated, reporting all rates to 1906-1910 birth-cohort. RESULTS: The mean annual mortality rates from PD sharply increased during the period of the study. The MRRs increased from the cohort born between 1881 and 1885, to a maximum in the cohort born between 1906 and 1910, and then markedly decreased in the following cohorts. CONCLUSION: According to our findings, the increase of PD mortality could be partly ascribed to an higher risk of dying from PD experienced by the cohorts of people born in the first decade of this century.

Cohort Studies↗
PubMed2005

Generation or birth cohort effect on cancer risk in Li-Fraumeni syndrome.

Genetic anticipation is the increased incidence, earlier onset, or increased severity of a disease in successive generations. Before the biological basis of anticipation had been demonstrated, the phenomenon was thought to be due to sampling bias, epigenetic effects, gene conversion, or recombinant events. Since then, the biologic basis for anticipation in a number of neurodegenerative disorders has been shown to be attributable to trinucleotide repeat instability, with expansion of repeats clearly correlated with an earlier age of onset. Recently, telomere shortening has been suggested as the mechanism for anticipation in the autosomal dominant form of dyskeratosis congenita, attributable to mutations in the TERC gene, leading to dysfunctional telomeres (Vulliamy et al. 2004). However, the pattern of anticipation has been observed in other disorders, including cancers, for which no genetic defect has been identified. In this study, we assess the apparent generation effect on cancer incidence in ten extended families with P53 germline mutation, identified through probands diagnosed with childhood sarcoma. The probands were from two sets of systematically ascertained sarcoma patients treated at the University of Texas M. D. Anderson Cancer Center between 1944 and 1982. From those overall studies, we have identified ten kindreds having germline P53 mutations in more than one generation. We compared the cancer incidence in members of successive generations of these families with P53 mutations (carriers) and with no P53 mutations (noncarriers). In carriers, cancer incidence increased in succeeding generations; there was no evidence for this effect in noncarriers; however, the noncarrier population was too small to rule it out. The apparent lack of increase in incidence in noncarriers argues against a cohort effect explaining the increase in carriers.

Adult↗
PubMed2001

Age, period, and cohort effects on the attitude toward supporting parents in Taiwan.

PURPOSE: Using the perspectives of age, period, and cohort (APC) effects, this study explored the changes in attitudes toward supporting parents in Taiwan. DESIGN AND METHODS: Population-representative cross-sectional data taken at 1984, 1990, and 1995 from the Social Change Survey in Taiwan were synthesized. Cohort tables and multi-nominal logistic regression were used to analyze the APC effects. RESULTS: Period and age effects were found in the change in attitudes toward supporting parents. Agreement on living with sons or children has slowly decreased. Younger persons agree more than older ones in attitudes toward parents living with their married son or children. There was a reduction in the differences among cohorts across periods. There was no demonstration of cohort effect in this study. IMPLICATIONS: The results indicate that for married children, living with parents is no longer popular in Taiwan society. Social policy should address the unmet needs of elderly people in assistance with daily living.

Adult↗
PubMed2001

Increasing thyroid cancer incidence in Canada, 1970-1996: time trends and age-period-cohort effects.

We examined time trends in thyroid cancer incidence in Canada by age, time period and birth cohort between 1970 and 1996. Age-specific incidence rates by time period and birth cohort were calculated and age-period-cohort modelling used to estimate effects underlying the observed trends. Overall age-adjusted incidence rates of thyroid cancer doubled, from 3.3 and 1.1 per 100 000 in 1970-72 to 6.8 and 2.2 per 100 000 in 1994-96, among females and males respectively. Almost all the increase between 1970-72 and 1994-96 was due to papillary carcinoma of the thyroid. Age, birth cohort and period effects significantly improved the fit of the model for females, while age and birth cohort effects were significant determinants of the incidence among males. There were significant differences in the patterns/curvature for age, period and birth cohort effects between women and men. Our results suggest that the increases in thyroid cancer incidence in Canada may be associated with more intensive diagnostic activities and change in radiation exposure in childhood and adolescence. Temporal changes in reproductive factors among young women may explain some of the gender differences observed.

Adolescent↗
PubMed2005

Methodologic issues in studies of mortality following epilepsy: measures, types of studies, sources of cases, cohort effects, and competing risks.

This paper addresses methodologic issues in studies of mortality, and the impact of these issues in studies of mortality in epilepsy. One important issue is to identify the question: Is it whether epilepsy increases the risk of dying? Or is it whether the underlying condition that led to epilepsy, itself associated with an increased risk for death, is the cause of increased mortality observed in epilepsy? Each measure for estimating mortality requires specific study designs. The mortality rate, case fatality, standardized mortality ratio (SMR) are calculated in prospective or retrospective cohort studies of death in epilepsy. Because the SMR is obtained by indirect standardization, it uses the age- and gender-distribution of the study group with epilepsy, which differs across studies. Thus, the SMR is impossible to compare across studies. The proportionate mortality ratio considers only the proportion of deaths that are due to epilepsy and is useful when denominators are unavailable, often the case in the developing world. Mortality studies in prevalent cohorts of people with epilepsy are compared to those in incident cohorts of epilepsy. The impact of different sources of cases on mortality in epilepsy is discussed. Finally, cohort effects and competing risks are examined. We conclude that the gold standard for studies on mortality should be a population-based cohort of incident cases. Only this type of cohort permits a complete collection of data and the observation of the clinical phase of the disease from the diagnosis of epilepsy to the outcome of the study, death.

Age Distribution↗
PubMed1998

Increasing incidence of testicular cancer--birth cohort effects.

The incidence of testicular cancer is rising in most Western populations. A collaborative study between nine population-based cancer registries in countries around the Baltic Sea was utilized in order to analyze in detail geographic variations and temporal trends in the occurrence of testicular cancer. There were 34,309 cases registered up until 1989 starting in Denmark in 1942 and most recently in Latvia in 1977. From the descriptive epidemiology it was obvious that there was a substantial variation in the age-standardized incidence amounting to about a 10-fold difference between the different countries ranging from 0.8 per 100,000 person-years in Lithuania to 7.6 per 100,000 person-years in Denmark. Previous studies have indicated that this increase is due to birth cohort effects. A more detailed analysis was therefore performed in those six countries with a sufficiently long period of cancer registration; Poland, former East Germany, Norway, Finland, Denmark and Sweden. This analysis showed that birth cohort is a more important determinant of testicular cancer risk than year of diagnosis. In Poland, former East Germany and Finland, there was an increasing risk for all birth cohorts. Among men born in Denmark, Norway or Sweden between 1930 and 1945, this increasing trend in risk was interrupted in these birth cohorts but followed thereafter by an uninterrupted increase by birth cohort. In conclusion, life time exposure to environmental factors which are associated with the incidence of testicular cancer appear to be more related to birth cohort than to year of diagnosis. Because testicular cancer typically occurs at an early age, major etiological factors therefore need to operate early in life, perhaps even in utero.

Adult↗
PubMed2003

Birth cohort effect of the mortality rate from congenital heart disease in Japan.

BACKGROUND: The mortality rate from congenital heart disease in Japan had decreased partly because the great improvement of medical treatment and care. Therefore, the patients who would have died of congenital heart disease in younger age in the past may be alive to be adult, and the number of adults with congenital heart disease might increase. If the management of such adults did not improve, the mortality rate from congenital heart disease might increase because of the increased number. METHODS: Using the Japanese vital statistics from 1960 through 1999, we observed the time series of the mortality rate from congenital heart disease by age and sex. The birth cohort consisted of those who were bone in 5-year period starting in 1960. The mortality rate was the sum of the number of death in every five years divided by the population of the center year. RESULTS: The transition of the mortality rate from congenital heart disease for age group 0 to 4 years was decreased since 1973. Other age groups showed decreased mortality rate since late 1960's. The birth cohort analyses showed that the mortality rate of each birth cohort was decreased as time passed, especially the age group 5 to 9 years old and 10 to 14 years old. CONCLUSION: Birth cohort effect of mortality from congenital heart disease exists in Japan.

Adolescent↗
PubMed1996

Time trend and age-period-cohort effect on incidence of thyroid cancer in Connecticut, 1935-1992.

Recent studies from Europe suggest a continuing increase in thyroid cancer, but it is unclear whether this trend also applies to the United States. The current study examined the long-term trend of thyroid cancer in Connecticut. Our results show that the overall age-adjusted incidence rate of thyroid cancer has been increasing in Connecticut, from 1.30/100,000 in 1935-1939 to 5.78/100,000 in 1990-1992 in females, and from 0.30/100,000 in 1935-1939 to 2.77/100,000 in 1990-1992 in males. The increase mainly comes from papillary carcinoma of the thyroid. The birth cohort analyses indicate that the increase in thyroid cancer occurred among cohorts born between 1915 and 1945, which experienced an increase of 31.4% every 5 years in males and 17.3% in females over the period 1960-1979. For those born since the 1945 cohort, the incidence has been decreasing, at rates of 9.3% and 8.3% every 5 years over the period 1975-1992 in males and females, respectively. Age-period-cohort modeling results also suggest a strong birth cohort effect on the observed time trend in both sexes, which closely follows the introduction of radiation treatment of benign childhood conditions in the head and neck between 1920 and the 1950s in the United States. Our results are consistent with the suggested radiation hypothesis, indicating that radiation treatment of benign childhood conditions in the head and neck is largely responsible for the observed increase of thyroid cancer in Connecticut.

Adenocarcinoma, Follicular↗
PubMed1998

Molecular epidemiology of HTLV-II among United States blood donors and intravenous drug users: an age-cohort effect for HTLV-II RFLP type aO.

Molecular subtyping was used to investigate the epidemiology of human T-lymphotropic virus type II (HTLV-II) in the United States. Nested polymerase chain reaction of the HTLV-II long terminal repeat region followed by restriction fragment length polymorphism (RFLP) analysis was performed on HTLV-II seropositive subjects including 97 U.S. blood donors without major risk factors for HTLV-II infection, 53 injection drug users (IDU), and 10 American Indian blood donors. Three new HTLV-II RFLP types were confirmed with DNA sequencing and phylogenetic analysis. HTLV-II RFLP type aO (Switzer classification) was associated with older age [adjusted odds ratio (OR) 1.06 per year of age, 95% confidence interval (CI) 1.02-1.09] and with Black (OR 5.24, 95% CI 1.90-14.47) and White (OR 4.43, 95% CI 1.67-11.75) race/ethnicity. These data are consistent with an age-cohort effect for HTLV-II RFLP type aO among older White and Black IDU and blood donors. This finding could be explained by an epidemic of non-aO HTLV-II RFLP types among younger persons of Hispanic and other race/ethnicity, superimposed upon endemic HTLV-II RFLP type aO among older Black and White persons.

Adolescent↗
PubMed1994

Time trend and the age-period-cohort effect on the incidence of histologic types of lung cancer in Connecticut, 1960-1989.

BACKGROUND: Recent epidemiologic studies have suggested changing patterns of lung cancer incidence by histologic type. The observed time trends have been attributed to a change in the rate of cigarette smoking, changes in exposure to new environmental carcinogens, and changes in the criteria for the histopathologic diagnosis of lung cancer. The current study was designed to examine the incidence patterns of lung cancer by histologic type in Connecticut and to use this information to project the future trend of the disease in this population. METHODS: This study was based on all the lung cancer cases reported to the Connecticut Tumor Registry between 1960 and 1989. On the basis of this data set, crude and age-adjusted incidence rates of lung cancer were calculated by histologic type for each sex. The age-specific incidence rates are presented by calendar year and cohort year of birth. A regression model was used to identify birth cohort, period, and age as determinants of the observed time trends. RESULTS: For the overall age-adjusted incidence rates, squamous cell carcinoma and small cell carcinoma have stabilized in men, whereas they are still increasing in women. The incidence of adenocarcinoma has been increasing in both men and women, but there has been a much sharper incidence among females since the mid-1970s. An examination of age-specific incidence rates by birth cohort and the results from age-period-cohort modeling indicate that incidences of all three major histologic types of lung cancer in the recent birth cohorts either have started decreasing (squamous cell carcinoma) or shown a clear reduction in the rate of increase (adenocarcinoma and small cell carcinoma). This study, however, did not indicate an increase of bronchoalveolar lung carcinoma, which was reported by other clinically based studies. CONCLUSION: While the overall age-adjusted incidence rates showed different incidence patterns for different histologic types of lung cancer, a decreasing or stabilized rate for all three major histologic types of lung cancer was observed in recent birth cohorts in both males and females. The observed incidence pattern is consistent with smoking trends over time including changes in smoking prevalence and the consumption of low tar and filter cigarettes. It is expected that if the current trend in tobacco smoking continues and if there are no major changes in other risk factors for lung cancer, a forthcoming stabilization or decrease in the rate of lung cancer incidence for all major histologic types (including adenocarcinoma) in both sexes in Connecticut could be anticipated.

Adenocarcinoma↗
PubMed2000

Cohort effect of HCV infection in liver cirrhosis assessed by a 25 year study.

BACKGROUND: The role of HCV infection in the development of chronic liver disease is still unclear. OBJECTIVES: Assess the presence of HCV infection in patients with liver cirrhosis. STUDY DESIGN: 123 cases of cirrhotic liver randomly selected over a 25 years period (1969-1994) from the autopsy archives of the Pathology Department of the University of Trieste, Italy, were analyzed for the presence of HCV viral genome. METHODS: Total RNA was extracted from formalin-fixed paraffin-embedded tissues of the cirrhotic liver. Genotype analysis for HCV was performed after RT-PCR by dot-blot hybridization with the three major genotype-specific probes (G1, G2 and G3). RESULTS: The overall HCV genome frequency was 50.4% (62/123). The positivity was quite constant in the 1969-1979 period (35-38%), rose to 65% in 1984, peaked to 77% in 1989 (P<0.005 vs. the previous decade), and decreased to 50% in 1994. HCV genotype G1 was found in 89% of the 62 positive samples. The mean age of death of HCV-positive and HCV-negative patients was comparable (69+/-12 vs. 67+/-16 years, NS). CONCLUSIONS: These data show an increasing frequency of HCV infection in cirrhotic liver tissues from 1969 to 1994, which peaked in 1989. The genotype G1 was the almost uniquely associated with cirrhosis. These findings indicate that the HCV infection occurred around the late 1950s-early 1960s, thus supporting the hypothesis of a cohort effect. HCV infection seems not to alter the natural history of liver cirrhosis as indicated by the comparable age at death of HCV positive and HCV negative patients.

Aged↗
PubMed1986

Age, period of death and birth cohort effects on suicide mortality in Italy, 1955-1979.

Trends in death rates from all suicides and specific methods of suicide in Italy over the period 1955-79 were analysed on the basis of age-specific and age-standardised rates, and through a log-linear Poisson model to isolate the effects of age, birth cohort and calendar period. In both sexes, a large decrease in mortality from suicide was evident in the late 1950's and early 1960's. Thereafter, death certification rates showed fluctuating trends up to the mid 1970's, when steady increases became evident for both sexes. Nevertheless, overall age-standardized mortality rates from suicide in the late 1970's were still considerably lower than in the two previous decades (15% in males, 7% in females). The observed variations in suicide mortality, mostly in males, can be explained in terms of period of death effect and be related to changes in the Italian economic situation. This view finds further support from analysis of age-specific trends (e.g. mortality rates in the younger age groups started rising in the early 1970's, together with a rise in unemployment rates among the young). Cohort curves for males born in the current century were U-shaped as well, with marked declines for generations born between 1905 and 1930, and moderate increases for more recent cohorts. For females, the cohort curve was remarkably flat. Some of the changes in the various methods of suicide can be explained in terms of well-defined exogenous factors (e.g., the large fall in poisoning by domestic gas is obviously attributable to domestic gas detoxification).

Adolescent↗
PubMed2005

Re-evaluation of randomized control trials of lithium monotherapy: a cohort effect.

OBJECTIVE: The reported reduction of lithium's efficacy in the prophylaxis of bipolar illness has been attributed to various factors, including diagnostic changes and heterogeneous study designs. We attempted to quantify the impact of pre-randomization enrichment designs and diagnostic drift on randomized controlled trials (RCTs) of lithium maintenance therapy. METHODS: Using the Cochrane RCT search filter, MEDLINE, EMBASE, and PSYCHINFO were searched (1966 to June 2004) for all available randomized studies using the text word 'lithium'. Studies of 1 year minimum duration in bipolar disorder involving lithium and placebo arms were identified. Superiority trials without a placebo arm, discontinuation and mirror image studies were excluded. Standardized scales were used to assess randomization and allocation concealment. RESULTS: Nine RCTs enrolling 1432 bipolar I and II patients, randomizing 341 to lithium and 386 to placebo were identified, with 705 reported pre-randomization dropouts. The pooled odds of remaining recurrence free in two non-enriched RCTS using Research Diagnostic Criteria (RDC) or Feighner criteria were 3.2:1 (95% CI 0.65--15.46) trending in favor of lithium over placebo, and 22.0:1 (95% CI 7.0--68.7) for three trials using lithium enrichment and excluding atypical bipolar disorder. The odds of remaining recurrence free using DSM-IV criteria and lamotrigine enrichment were 1.9:1 (95% CI 1.2-2.8). CONCLUSION: Lithium maintenance RCTs differ in patient selection, design, and outcome. A cohort effect can be associated with the use of pre-randomization enrichment phases and, to a lesser extent, with diagnostic drift, compromising straightforward comparisons across three decades of lithium monotherapy in bipolar illness.

Antipsychotic Agents↗
PubMed1989

Age, period and cohort effects on the risk of major depression: results from five United States communities.

Rates of major depression are presented from the recently completed Epidemiologic Catchment Area (ECA) Study based on probability samples of over 18,000 adults, 18 years of age and older, living in five U.S. communities. These rates were analyzed to describe simultaneously the changes affecting successive birth cohorts and the changes associated with the period in which the onset of the disorder occurred, using age-period-cohort (APC) models. The non-identifiability problem inherent in all APC models was resolved by assuming that the linear period effect and linear cohort effect were non-negative. This assumption is consistent with our a priori substantive knowledge of the disease. Under this assumption, as the linear period effect varies from its minimum to its maximum values, a family of curves representing the possible effects of a factor was generated for each of the time factors--age, period and cohort. The results of the analysis showed a sharp increase in rates of major depression among both men and women in the birth cohort born during the years 1935-1945. The rates among females, however, seemed to have stabilized in the generations born since 1945, while the rates in males continued to rise sharply among the cohorts born in the following decade, after which, in 1955, they also levelled off. In contrast, the rates associated with period of onset of major depression continued to increase between the years 1960-1980 among both men and women of all ages studied. These findings are considered in light of the persistent concentration of depression in women and in biologically related members of families of affected individuals.

Adolescent↗
PubMed1999

Homicide mortality in the United States, 1935-1994: age, period, and cohort effects.

The authors analyzed homicide mortality data for the United States from 1935 to 1994, to delineate temporal trends and birth cohort patterns. This study included 850,822 homicide-attributed deaths documented by the National Center for Health Statistics, and incorporated graphical presentation, median polish, and Poisson regression modeling in an age-period-cohort analysis. Death rates from homicide in the United States doubled in the past four decades, with most of the increase having occurred during the 1960s and early 1970s. Poisson regression models confirmed that the rise of homicide mortality in both men and women was largely attributable to a significant period effect between 1960 and 1974. No discernible cohort patterns were found among women. However, homicide rates for recent male birth cohorts appeared to peak at younger ages and at higher levels. A significant increase in homicide mortality risk beginning with males born around 1965 was found by examining the residuals of median polish, and the second-order changes in the regression coefficients from the age-period-cohort model. The hike of homicide mortality during 1985 and 1994 was explained by this cohort effect. Increased prevalence of substance abuse and availability of firearms are two likely factors underlying this disturbing cohort pattern.

Adolescent↗