Period analysis and cohort analysis of marriage and fertility among Chinese women.
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Suicide and age in Alberta, Canada, 1951 to 1977. A cohort analysis.
A cohort analysis was undertaken of the 4,315 deaths by suicide registered in Alberta, Canada, Vital Statistics between the years of 1951 and 1977, inclusive. Age, gender, and year of death were available in all but two instances. Five-year age cohorts were identified and their suicide rates were followed as the cohorts aged. Analyses were done for men and women separately and combined. Suicide rates increased directly with age, regardless of gender for each cohort observed. Once a cohort entered the 15- to 19-year-old age range with a high rate of suicide, the rate for that cohort remained consistently high as it aged.
Adolescent↗
On the age-period-cohort analysis of suicide rates.
Cohort analysis has become a popular method of examining national trends in suicide rates. Most of the studies investigating this phenomenon have reported a cohort effect to be present. Using a graphical approach, this paper places cohort analysis within the broader framework of age-period-cohort analysis. It is shown that published reports may have failed to identify cohort effects due to using only portions of the available data. With a simple mathematical model it is demonstrated that what appears to be a cohort effect may be a period effect, and conversely. It is recommended that suicide rates be examined for both period and cohort effects before conclusions are drawn regarding trends, and that the complete data set be used for this purpose.
Adolescent↗
Long adult deformity fusions to L5 and the sacrum. A matched cohort analysis.
STUDY DESIGN: A matched cohort analysis of long adult deformity fusions according to distal fusion level (L5 vs. S1). OBJECTIVE.: To compare the results of long adult deformity fusions to either L5 or the sacrum in the presence of a "healthy" 5-1 disc using a matched cohort analysis. SUMMARY OF BACKGROUND DATA: For adult spinal deformity, the decision often arises whether to terminate a long fusion at L5 or the sacrum. The decision is especially challenging in the presence of a "healthy" (Grade 0 to 1 degeneration) 5-1 disc. MATERIALS AND METHODS: A total of 95 adult deformity patients that underwent fusion from the thoracic spine to either L5 or the sacrum were sorted according to five preoperative criteria: 5-1 disc status, patient age, smoking status, number of levels fused, and sagittal balance. Two cohorts (L5, 27 patients; sacrum, 12 patients) were precisely matched according to the five criteria. Patients were evaluated at 2-year minimum follow-up according to radiographic data, complications, and SRS-24 outcomes. RESULTS: Correction of sagittal imbalance was superior for sacrum patients (C7 plumb line: L5, 0.9 cm; sacrum, 3.2 cm; P = 0.03). At latest follow-up (L5, 5.2 years; sacrum, 3.7 years), 67% of L5 patients had radiographic evidence of advanced 5-1 disc degeneration and the L5 cohort tended to have inferior sagittal balance (C7 plumb line: L5, +4.0 cm; sacrum, +1.2 cm; P = 0.06). The sacrum cohort, however, required more surgical procedures (L5, 1.7; sacrum, 2.8; P = 0.03) and experienced a greater frequency of major complications (L5, 22%; sacrum, 75%; P = 0.02), including nonunion (L5, 4%; sacrum, 42%; P = 0.006) and medical morbidity (L5, 0%; sacrum, 33%; P = 0.001). SRS-24 scores reflected a similar patient assessment of outcome and function for the two cohorts (L5, 89; sacrum, 87). DISCUSSION AND CONCLUSION: At 3 to 5 years' mean follow-up, long adult fusions to the sacrum required more procedures and had a higher frequency of complications than similar fusions to L5. For fusions to L5, subsequent subjacent disc degeneration is common and may be associated with a forward shift in sagittal balance. The ultimate influence of these factors on long-term outcomes remains to be seen.
Adult↗
Cohort analysis of mortality rates as an historical or narrative technique.
A history of cohort analysis has been given, and it has been pointed out that the bulk of the literature on the subject has dealt with concepts that assume either that graduation and possibly extrapolation are desirable, preferably in conformity with some formula expressing what is implicitly accepted as a "law of mortality", or that, whether or not a fixed pattern of mortality exists, the intensity of mortality risk is largely determined in early life. The view is advanced that either concept alone, is, or both concepts together are, inadequate and may lead to an improper assessment of the nature-nurture complex, since environment and therapeutic measures are constantly changing. The plea is made for the technique of cohort analysis to be used as a narrative or historical technique, and for a synthesis of knowledge derived from social history, medical history, and cohort analysis to be made to interpret the narrative. The effects of a changing rate on the mortality pattern as depicted by date-contour analysis and cohort analysis are outlined and the danger of basing biological theories on the mortality pattern revealed by date-contour analysis alone is indicated. This point is illustrated by reference to a recent theory that has been based on such an analysis.
Age Distribution↗
An alternative approach to statistical age-period-cohort analysis.
Age-period-cohort analysis has generated considerable interest in epidemiology, but the model has fundamental problems which have been discussed by Kupper et al. While one can agree that the age-period-cohort model should be used with caution, it should also be noted that some useful inferences can be made with the model. The problems raised by Kupper et al. are discussed in terms of estimable functions of the parameters, which are not affected by arbitrary constraints on the parameters. The use of these methods are illustrated and specific examples presented where age-period-cohort models can be used effectively.
Aging↗
Corpectomy versus laminoplasty for multilevel cervical myelopathy: an independent matched-cohort analysis.
STUDY DESIGN: Matched patient cohorts using retrospective chart and radiographic review with independent clinical and radiographic follow-up were reviewed. OBJECTIVE: To compare the clinical and radiographic outcomes of multilevel corpectomy and laminoplasty using an independent matched-cohort analysis. SUMMARY OF BACKGROUND DATA: The treatment of choice for multilevel cervical myelopathy remains a matter of investigation. For the decompression of three or more motion segments, multilevel corpectomy and laminoplasty have proven effective while avoiding the pitfalls of laminectomy. Direct clinical comparisons of these two procedures are few in number and are limited by the heterogeneity in their patient groups. METHODS: Medical records of all patients treated for multilevel cervical myelopathy with either multilevel corpectomy or laminoplasty between 1994 and 1999 at the Emory Spine Center were reviewed. From a pool of 38 patients meeting stringent inclusion and exclusion criteria, 13 patients who underwent multilevel corpectomy were blindly matched with 13 patients who underwent laminoplasty based on known prognostic criteria. A single physician independently evaluated each patient and their radiographs at their latest follow-up appointment. RESULTS: The cohorts were well matched by age, duration of symptoms, severity of myelopathy (Nurick grade), and preoperative sagittal alignment (C2-C7). Mean operative time, blood loss, and hospital stay were nearly identical. The mean follow-up for multilevel corpectomy and laminoplasty were 49 and 40 months, respectively. Improvement in function averaged 1.6 Nurick grades after laminoplasty and 0.9 grades after multilevel corpectomy (P > 0.05). Subjective improvements in strength, dexterity, sensation, pain, and gait were similar for the two operations. The prevalence of axial discomfort at the latest follow-up was the same for each cohort, but the analgesic requirements tended to be greater for patients who underwent multilevel corpectomy. Sagittal motion from C2 to C7 decreased by 57% after multilevel corpectomy and by 38% after laminoplasty. One complication (C6-C7 herniated nucleus pulposus [HNP] requiring anterior discetomy with fusion) occurred in the laminoplasty group. Multilevel corpectomy complications included progression of myelopathy, nonunion, persistent dysphagia, persistent dysphonia, and subjacent motion segment ankylosis. CONCLUSIONS: Both multilevel corpectomy and laminoplasty reliably arrest myelopathic progression in multilevel cervical myelopathy and can lead to significant neurologic recovery and pain reduction in a majority of patients. Surprisingly, the laminoplasty cohort tended to require less pain medication at final follow-up than did the multilevel corpectomy cohort. Given this and the higher prevalence of complications among multilevel corpectomy patients, it is believed that laminoplasty may be the preferred method of treatment for multilevel cervical myelopathy in the absence of preoperative kyphosis.
Adult↗
Incidence of retinoblastoma from 1958 to 1998 in Northern Europe: advantages of birth cohort analysis.
PURPOSE: To assess change in incidence of retinoblastoma in Northern Europe and to compare commonly used methods for calculating its incidence against birth cohort analysis. DESIGN: Retrospective cohort study. PARTICIPANTS: Individual and pooled data of 291 Swedish and 174 Finnish children diagnosed with retinoblastoma between 1958 and 1998. MAIN OUTCOME MEASURES: Incidence per 1 million children younger than 5 years of age (37 812 035 person- years at risk) and per 100 000 live births (7 152 265 live-born children at risk). METHODS: Data were from Swedish and Finnish Cancer Registries and corresponding national referral centers for retinoblastoma. Incidence was calculated both by standard analysis per children younger than 5 years of age and per live births, and by birth cohort analysis. Curves were smoothed with robust, locally weighted regression. Linear regression was used to fit pooled data. RESULTS: The number of new retinoblastoma cases per year ranged from 0 to 13 (1-13 per birth cohort) in Sweden and from 0 to 10 in Finland (1-9 per birth cohort). The mean incidence was 11.8 (95% confidence interval [CI], 10.5-13.1) and 11.2 (95% CI, 9.4-13.0) per 1 million children younger than 5 years of age in Sweden and Finland, respectively, and 6.7 (95% CI, 5.9-7.5) and 6.2 (95% CI, 5.3-7.2) per 100 000 live births, respectively. Analysis based on year of diagnosis suggested moderate increase in incidence since 1990, but by birth cohort analysis, incidence rates were stable for both countries. The pooled incidence by birth cohort was 6.0 (95% CI, 5.4-6.6) per 100 000 live births, corresponding to 1 in 16 642 (95% CI, 15 105-18 528) live births. CONCLUSIONS: The data suggest that the incidence of retinoblastoma is stable in Northern Europe. Analysis based on birth cohort is recommended for future epidemiologic studies, because it minimizes the effect of variable age at diagnosis of this developmental cancer and results in less variable incidence rates than standard analysis based on year of diagnosis.
Adolescent↗
[A single year birth cohort analysis of mortality in Japan, 1950 to 1984, statistical method and all cause mortality].
Mortality of single birth year cohort were calculated using the data tape of Information Service on World Health Statistics, WHO, 1950-1984. The data tape gave population and number of deaths for each year of age under 5 years of age and by 5 years of age for ages from 5 to 84 years. Population and number of deaths by age for each year of age in each calendar year were estimated by interpolation. Populations for each year of age were interpolated by B-spline interpolation. Number of deaths for each year of age were calculated by application of "two dimensional semi-Hermite method" after estimation of number of deaths for age 80, 81,......84, using Sprague interpolation factors. Age-specific cohort mortality curves were lower for each successive cohort, demonstrating the so-called "cohort phenomenon", clearly. Ratios of mortalities at the same age, for each successive 5 year interval cohort, which indicate cohort-by-cohort changes of mortalities, were thus less than 1.0 in almost all age groups. In recent years the ratios have gradually been leveling off at 0.8-0.9. Cohorts born in the early Showa Era (around 1930) showed higher ratios than all other cohorts, indicating relatively poor improvement in mortalities compared to the other cohorts. Ratios of cohort mortalities for successive ages within the same cohort, which indicates mortalities increase with advance of age, were greater than 1.0 after adulthood. These particular results showed that the increase in mortality with age accelerated after 30 years of age and that a difference in trend was observed between male and female after age 50. This new method of cohort analysis, single birth year cohort, gives clearer results than those obtained by methods heretofore utilized in cohort studies and is useful for more detailed analysis of cohort mortality.
Adolescent↗
Birth cohort analysis of suicide mortality in Belgium 1954-1981 by a graphic and a quantitative method.
The effect of birth cohort upon the recent increase in Belgian suicide trends was analyzed by two techniques: a graphic display and an Age-Period-Cohort (APC) modelling procedure. Both suggest an analogous pattern: suicide mortality steadily increased within successive male cohorts born after 1920 and within female cohorts born even before 1900. Between 1970 and 1980, period related factors seem to have operated independently. Every technique of cohort analysis however has important interpretational limitations because of the variable interplay between age period and cohort factors. As a consequence, explanations remain very tentative, Notwithstanding its rather poor etiological power in suicide epidemiology, cohort analysis is very useful in the more accurate description and prediction of suicide trends.
Adolescent↗
Mortality from cancer of the digestive system in Italy: 1950-1975 cross-sectional rates and cohort analysis.
In this study of mortality from cancer of the digestive system in Italy, 1950-1975, both cross-sectional rates and cohort analysis were used. The study found that in both sexes age-standardized rates for cancer of the colon, rectum, liver and biliary tract, and pancreas are increasing whereas the rates for cancer of the stomach are decreasing. Rates for esophagus cancer have remained fairly constant. Cohort analysis showed different trends for selected sites. As to cancer of the stomach, for both sexes, cohorts born up until about 1881 have constant or increasing rates; cohorts born after 1881 have declining rates. For cancer of the esophagus in males the rates reach a peak in the 1896 birth-cohort; cohorts born prior to 1896 show an increase in rates and cohorts born later show a decline. For cancer of the colon, liver and biliary tract, and pancreas, the rates rise constantly for all ages and all cohorts in both sexes. The rates for cancer of the rectum rise after age 75 whereas below that age the rates tend to level off and decline.
Adolescent↗
Cohort analysis of lung cancer in the Netherlands.
A cohort analysis of lung cancer mortality in the Netherlands from 1936--1974 is presented. Apart from small corrections, age-specific lung cancer mortality rates can be expressed as the product of a cohort (generation) factor and an age factor. The cohort factors increase until the 1930 birth cohort, after which there is a rapid decline. The age-risk factors increase smoothy with age. Age-specific incidence curves of past and future years will follow the curve of the age-risk factors provided that the cohort-risk factors are unchanging. The method can be applied to other chronic diseases.
Adult↗
Trends in alcohol-related mortality in Sweden 1969-2002: an age-period-cohort analysis.
AIM: To study the effects of age, period and cohorts on alcohol-related mortality trends in Sweden. DESIGN: The study comprises an age-period-cohort analysis. SETTING AND PARTICIPANTS: The analysis was based on all deaths in the Swedish population between 1969 and 2002. MEASUREMENTS: Data on alcohol-related deaths in Sweden from 1969 to 2002 excluding accidental injury and homicide were used. The analysis covered 43 021 deaths. FINDINGS: Time period and birth cohort both influenced alcohol-related mortality. Male cohorts born in the 1930-40s exhibited the highest alcohol-related mortality, while for females those born in the 1940-50s had the highest alcohol-related mortality. For both men and women, those born in the 1960-70s had the lowest age-adjusted alcohol-related mortality. High-risk cohorts were young or in early adulthood during the periods that alcohol became more available in Sweden. The low-risk cohorts of the 1960-70s were brought up during a period when society was concerned with increasing alcohol problems and more emphasis was placed on issuing alcohol awareness information in schools. CONCLUSIONS: Cohort effects were found suggesting that the link between alcohol consumption and non-accident alcohol-related mortality at the population level is dependent on other factors that may change over time. One such factor may be that restrictive alcohol policies have a greater effect on drinking in those who are younger at the time they are put into effect.
Adolescent↗
Cohort analysis of suicide rates in Australia.
Age-specific cohort analysis of Australian suicide rates confirmed recent Canadian and American reports of a substantial increase in suicide rate among young age groups. However, it was unable to replicate fully the previous findings that not only did successive birth cohorts have higher suicide rates, but that at each successive five-year period they had higher suicide rates than preceding cohorts had at that age. The major differences could be explained on the basis of the introduction of legislation that restricted the prescription of sedatives. This suggests that although there may be early and lasting effects on successive birth cohorts contributing to a general increase in cohort-specific suicide rates in the countries examined, such rates also can be influenced by changing environmental factors more immediately related to the suicide itself.
Adolescent↗
Analysis of mortality data from the former USSR: age-period-cohort analysis.
The objective of this article is to review research on age-period-cohort (APC) analysis of mortality and to trace the effects of contemporary and historical factors on mortality change in the former USSR. Several events in USSR history have exerted a lasting influence on its people. These influences may be captured by an APC model in which the period effects measure the impact of contemporary factors and the cohort effects the past history of individuals which cannot be attributed to age or stage in the life cycle. APC models are extensively applied in the study of mortality. This article presents the statistical theory of the APC models and shows that they belong to the family of generalized linear models. The parameters of the APC model may therefore be estimated by any package of loglinear analysis that allows for hybrid loglinear models.
Adolescent↗
Is quarterly cohort analysis useful for assessing treatment outcomes in a low incidence country?
SETTING: In the Czech Republic, a country regarded as having a low incidence of tuberculosis (TB), short-course chemotherapy (SCC) of TB has been implemented in routine practice country-wide. OBJECTIVE: To assess the outcome of SCC by quarterly cohort analysis of patients using the methodology recommended by the World Health Organization (WHO). DESIGN: Patients with newly detected bacteriologically confirmed pulmonary TB notified in 1998 were treated according to local recommendations (SCC) or with the WHO-recommended DOTS strategy. The type of chemotherapy and its outcome were evaluated 12 months later by quarterly cohort analysis. RESULTS: A total of 731 patients with bacteriologically confirmed pulmonary TB, 403 of them smear-positive, were assessed. The proportion of those treated under the DOTS strategy increased from 56.2% to 75.1%. Favourable treatment outcomes (cure or treatment completed) were achieved in 69.0% of patients in the first quarter and 74.0% in the fourth quarter. Only four treatment failures and 21 defaulters were recorded. A total of 129 patients (15-21% in different cohorts) died before or during treatment, mostly from causes not connected with TB. If this proportion were not taken into account, treatment efficacy would have attained 85%. CONCLUSIONS: Analysis of SCC based on quarterly cohorts proved feasible in routine conditions in a country with a low incidence of TB and ongoing TB control, and provided more information than once yearly analysis.
Adult↗
Significant difference in the trends of female breast cancer incidence between Taiwanese and Caucasian Americans: implications from age-period-cohort analysis.
Female invasive breast cancer (FIBC) in Taiwan is characterized by a striking recent increase of incidence and a relatively young median age (45-49 years) at diagnosis. The Westernization of lifestyle that is increasingly affecting younger generations of Taiwanese may have an important impact on this change. We compared epidemiologic data on FIBC in Taiwanese obtained from the Taiwan Cancer Registry with data for Caucasian Americans obtained from the database of the Surveillance, Epidemiology, and End Results Program for the period from 1980 to 1999. Age-specific incidence rates of FIBC were plotted by calendar year at diagnosis and by birth cohort for both populations. The individual effects of time period and birth cohort on the incidence trends of FIBC in both populations were evaluated using the age-period-cohort analysis. The incidence rate of FIBC was continuously increased in Taiwanese throughout the past 2 decades, whereas the increase of incidence was slowing down in Caucasian Americans. The incidence rates in Taiwanese women born after the 1960s were approaching that of Caucasian Americans. The age-period-cohort analysis showed a much stronger birth cohort effect on the incidence trend of FIBC in Taiwanese than in Caucasian Americans. This strong birth cohort effect corresponded to the Westernization of lifestyle in Taiwan since 1960. These findings indicate that a continued shift in the incidence and age distribution pattern of FIBC in Taiwanese toward that of Caucasian Americans should be anticipated.
Adult↗