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An automated program to calculate life tables of cumulative patency on a personal computer is described. This program can be set up quickly, and the tables can be displayed graphically and are automatically updated as new information is added.
OBJECTIVES: To estimate the cost effectiveness of statins in lowering serum cholesterol concentration in people at varying risk of fatal cardiovascular disease and to explore the implications of changing the criteria for intervention on cost and cost effectiveness for a purchasing authority. DESIGN: A life table method was used to model the effect of treatment with a statin on survival over 10 years in men and women aged 45-64. The costs of intervention were estimated from the direct costs of treatment, offset by savings associated with a reduction in coronary angiographies, non-fatal myocardial infarctions, and revascularisation procedures. The robustness of the model to various assumptions was tested in a sensitivity analysis. SETTING: Population of a typical district health authority. MAIN OUTCOME MEASURE: Cost per life year saved. RESULTS: The average cost effectiveness of treating men aged 45-64 with no history of coronary heart disease and a cholesterol concentration > 6.5 mmol/l for 10 years with a statin was 136,000 pounds per life year saved. The average cost effectiveness for patients with pre-existing coronary heart disease and a cholesterol concentration > 5.4 mmol/l was 32,000 pounds. These averages hide enormous differences in cost effectiveness between groups at different risk, ranging from 6000 pounds per life year in men aged 55-64 who have had a myocardial infarction and whose cholesterol concentration is above 7.2 mmol/l to 361,000 pounds per life year saved in women aged 45-54 with angina and a cholesterol concentration of 5.5-6.0 mmol/l. CONCLUSIONS: Lowering serum cholesterol concentration in patients with and without preexisting coronary heart disease is effective and safe, but treatment for all those in whom treatment is likely to be effective is not sustainable within current NHS resources. Data on cost effectiveness data should be taken into account when assessing who should be eligible for treatment.
Previous studies have failed to estimate the size of population at risk and underestimated the incidence of varicella among susceptible population. In this study, we calculated the incidence of varicella and its complications in Taiwan based on a life table method, in which the size of population at risk was taken into account. Population-based data were obtained from the Bureau of National Health Insurance. The age-specific incidences estimated by the uncorrected and corrected methods were compared. The incidence of varicella increased sharply after infancy and peaked at 16.7% in children aged 5 years. A correction which assumes the introduction of varicella vaccine resulted in a higher incidence of 19.5% in children aged 5 years. The lifetime cumulative incidence increased to around 76%. Sensitive surveillance of varicella and correct incidence estimate among susceptible population are essential in countries that have implemented or are about to implement varicella vaccination.
This article describes the association between total cholesterol to high-density lipoprotein (HDL)-cholesterol ratios and all-cause mortality in a large cohort of Americans with nearly 17 years of follow-up. Detailed actuarial life table methodology was used. It concludes that the relationship is best described as a J-shaped curve.
Quantitative health impact assessments of chronic mortality, where the impacts are expected to be observed over a number of years, are complicated by the link between death rates and surviving populations. A general calculation framework for quantitative impact assessment is presented, based on standard life table calculation methods, which permits consistent future projections of impacts on mortality from changes in death rates. Implemented as a series of linked spreadsheets, the framework offers complete flexibility in the sex specific, age specific, and year specific patterns of baseline mortality death rates; in the predicted impacts upon these; in the weights or values placed on gains in life; and in the summary measures of impact. Impacts can be differential by cause of death. Some examples are given of predictions of the impacts of reductions in chronic mortality in the populations of England and Wales and of Scotland.
The biology and life table parameters of Agistemus industani Gonzalez, A. cyprius Gonzalez, and A. floridanus Gonzalez (Acari: Stigmaeidae) were studied under laboratory conditions using two food sources: Panonychus citri (McGregor) eggs or ice plant, Malephora crocea (Jacquin) Schwantes pollen at 25 degrees C. The larval, protonymph, deutonymph, and adult stages of A. industani fed on citrus red mite eggs. All active stages of A. industani, except the larva, fed on all P. citri stages and the larval stage could not feed on P. citri adults. All immature stages of A. industani fed on M. crocea pollen. Agistemus cyprius larvae fed on P. citri eggs and larvae or ice plant pollen. The nymphal stages fed on P. citri eggs, larvae, and protonymphs but not deutonymphs or adults while A. cyprius deutonymphs and adults fed on all P. citri stages. Adult and nymphal stages of A. cyprius fed on ice plant pollen and successfully completed their development while A. floridanus did not. Agistemus floridanus larvae fed only on P. citri eggs, while the other stages fed on P. citri eggs, larvae, and protonymphs. The developmental times from egg to adult for A. industani and A. cyprius when fed M. crocea pollen were 11.3 and 13.4 days, respectively. Agistemus floridanus was unable to complete its life cycle on a diet of only M. crocea pollen. Agistemus industani, A. cyprius, and A. floridanus completed development from egg to adult in 11.7, 13.8, and 10.8 days, respectively, when fed P. citri eggs. The intrinsic rate of increase (r(m)) values for A. cyprius and A. industani were 0.0311 and 0.1201 per day on the pollen diet. The net reproductive rate (Ro) was 3.58 for A. cyprius and 10.07 for A. industani with generation times (T) of 45.2 and 35.1 days, respectively, on the ice plant pollen diet. The r(m) values for A. cyprius, A. floridanus, and A. industani on the P. citri egg only diet were: 0.0562, 0.1001, and 0.1031 per day, respectively. The Ro values for each species fed P. citri eggs only were: 6.36, 7.90, and 18.70 for A. cyprius, A. floridanus, and A. industani and the generation times (T) for each of the three species were: 35.2, 29.9 and 37.8 days, respectively.
The medical and demographic literature contain two popular formulae for the construction of cause-deleted life table lx values, one developed for applications in follow-up studies and the other for cross-sectional studies. It turns out that for both types of applications one of the two formulae is virtually always of better quality than the other. A formula developed by Keyfitz and Frauenthal is usually better than either.
The primary objective of this study was to estimate the survival function for time to onset of dementia in initially unaffected twins from when their partner (index proband) was diagnosed with dementia of the Alzheimer's type. Survival functions generated by life table analyses were compared by zygosity and gender. Sixty-one twin pairs where at least one member had been diagnosed with dementia of Alzheimer's type were included in the analyses. Additionally, both members of the twin pair had to be alive at the time the index proband was diagnosed with dementia. The probability of remaining cognitively intact within the first three years after the proband was diagnosed was high (0.93, 95% CI 0.89, 1.0), but after 15 years the probability of remaining intact was low (0.34, 95% CI 0.16, 0.52). Age of onset of the index proband was a significant covariate in the survival functions. There were significant differences in the survival functions for monozygotic (MZ) and dizygotic (DZ) co-twins (chi2 = 3.86, 1, P < 0.05), evidencing a genetic component for age of onset for dementia, but there were no significant differences between men and women.
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The trend of divorces has been usually evaluated by the divorce rate. However, it is difficult to make detailed analyses of the trend of or relevant factors concerning divorces by the divorce rate, because the denominator of this index is not a population at risk of divorces. The application of the life-table method to calculation of cumulative incidence rate of divorces for a birth cohort based on vital statistics data was introduced and its problems were discussed. This method was able to give a precise incidence rate of divorces and made it possible to examine the relationship of marital durations, generation of cohorts or age at marriage to the incidence of divorces. The results obtained were as follows: 1. The cumulative incidence rate of divorces increased and the marital duration-specific incidence rate of divorces decreased with continuation of marriages. 2. The cumulative incidence rate of divorces was higher in younger birth cohorts than in older cohorts. 3. The cumulative incidence rate of divorces was the lowest in the cohort married when the husband was 23 to 32 years of age than in the cohorts with other ages at marriage in all the birth cohorts examined.
BACKGROUND & OBJECTIVES: Vector control will for sometime remain a primary weapon in the war against vector borne diseases. Malaria is of paramount importance in this with its associated high morbidity and mortality especially in sub-Saharan Africa. This study on generational mortality associated factors in Anopheles mosquitoes life-table analysis was designed to investigate the fecundity, levels of mortality and mortality associated factors at the aquatic stages of anopheline malaria vectors. METHODS: Mortality associated factors were investigated at the eggs, I and II instar larval, III and IV instar larval and pupal stages of two anopheline species--Anopheles pseudopunctipennis (Theobald) and An. gambiae life-cycles in screen cages. Adult male and female mosquitoes were membrane filter-fed and algae in culture medium formed the bulk of food substances for the larval stage. Environmental temperature of culture media, pH and some associated physio-chemical factors were also determined. RESULTS: Results showed significant mortality rates at various aquatic stages. Infertility, cannibalism and environmental factors were the major factors responsible for mortality at the egg, larval and pupal stages respectively. INTERPRETATION & CONCLUSION: The aquatic stages of Anopheles mosquito mortality factor K and the mortality factors at the various stages investigated k1, k2, k3 and k4 are discussed. Our recommendations include further studies on the possible genetic modification of predacious An. pseudopunctipennis larvae and/or its modification for the production of sterile/infertile eggs as possible alternatives in the reduction and control of anopheline malaria burden.
The BEIR IV report gives graphs and tables that are used to estimate the risks due to radon (222Rn) and its decay products. The BEIR IV hypothesis predicts that the lifetime risks will depend upon the "normal" incidence of fatal lung cancers for nonsmokers and smokers and the life expectancies of both groups. This paper examines the influence of recent information on these health risks. The factors considered are a) the life tables for both sexes and for those who never smoked, formerly smoked, are currently light smokers, or are currently heavy smokers, and b) the age-dependent fatal lung cancer rates for the same groups of people. In general, the calculations indicate that people who have never smoked would have the same risks as those listed in the BEIR IV report as nonsmokers. For males, those who smoke or formerly smoked would have calculated risks that are greater than people who never smoked; however, for males, the smokers and former smokers considered in this paper have lower calculated risks than the BEIR IV smokers. For females, the heavy smokers examined here would have greater calculated risks than the BEIR IV smokers. The reasons for these differences are presented.
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Mercury is highly toxic to a variety of aquatic organisms including zooplankton. The functioning of freshwater ecosystems can be altered if rotifers, being a natural food link between phytoplankton and fish larvae, are contaminated by mercuric compounds. In order to detect age-specific responses of the rotifer Brachionus calyciflorus to mercury toxicity (5 nominal concentrations as chloride viz. 0, 0.000625, 0.00125, 0.0025 and 0.005 mg l(-1)), we used the standard life table method at two different food (Chlorella vulgaris) levels (0.5 x 10(6) and 1.5 x 10(6) cells ml(-1)). Data indicated that increase in mercury concentration had an increasingly intense negative effect on many of the life history variables, while at higher food levels, its impact was less. A nearly rectangular survivorship pattern was obtained in controls, especially at higher food levels. This trend gradually changed to a steep fall as the concentration of the heavy metal in the medium increased from 0 to 0.005 mg l(-1). At any given food density, increase in the mercury concentration resulted in decreased age-specific reproduction. A maximum of 3.5 offspring female(-1) was observed in controls at higher food density. The average lifespan varied from 6 to 8 days at low food level, depending on the heavy metal concentration in the medium. The corresponding values at high food level varied from 8 to 12 days. Regardless of mercury concentration in the medium, gross and net reproductive values varied from 10 to 33 and 4 to 19 offspring female(-1). The longest generation time (about 9 days) of B. calyciflorus was obtained at 1.5 x 10(6) cells ml(-1) food density in control, while the shortest was 5 days at low food level and high (0.005 mg l(-1)) mercury concentration in the medium. Depending on the food level and heavy metal concentration in the medium, the rate of population growth (r) varied from 0.32 to 0.62 d(-1). In general, higher food level resulted in higher r. Except generation time, all other derived variables were significantly influenced by food level and the heavy metal concentration in the medium.
The prevalence of ascariasis is very high in parts of rural areas in southern China. The high prevalence of ascariasis is one of the most neglected public health problems. A longitudinal investigation on the prevalence of ascariasis in a rural community in China was reported previously. In this article, we re-analyze the reported age specific prevalence of ascariasis using a life table method. The results from our analysis may provide a better summary of the impact of the disease on the studied population.
The efficacy indices of two representative sunscreen preparations were determined using life table analysis of individual sun protection factors (SPF), obtained by exposing a group of subjects to ultraviolet radiation (UVR) doses from 4 to 20 multiples of the control minimal erythema dose (MED). The ultimate efficacy index is expressed as the UVR dose under which a selected percentage of the population is safely protected by a sunscreen. This method takes into account several sources of bias in the current test procedure, in particular the considerable variability in individual responses. It also takes into account subjects in whom the MED of the protected skin is either higher or lower than the range of challenge doses to which they were exposed, thereby increasing the effective sample size. This method provides a more precise and comprehensive index of sunscreen protection, and enables statistical comparison of different preparations, or of the effect of other factors on their efficacy.
The variability in the numbers of treatment cycles couples may undertake with assisted reproductive technology (ART) and the length of time they may have to wait between successive cycles of treatment make the evaluation of treatment efficacy and prognosis complicated. The cumulative pregnancy rate using the life table method of analysis is being used more frequently to estimate the effectiveness of treatment. Although this approach is valid in some areas of infertility research, its use in ART is not appropriate, because the factors necessary for the analysis (particularly the scale for measuring the passage of time and lack of informative censoring) are not satisfied. Consequently, an overestimation of the effect of treatment is produced that may lead to biased decision making. Although there is no easy solution to this problem, several options for summarizing the outcome data are offered: pregnancy rate per cycle, time-limited analysis using proportions, conservative cycle-based cumulative pregnancy rate and real-time-based cumulative pregnancy rate. In this manner, more realistic information can be generated to counsel patients, evaluate the efficacy of treatments, compare rates among centres and guide the formulation of policies for infertility management and resource allocation.
The proportional hazards life table is a recently developed approach to the analysis of survival data when mortality risks vary among individuals. It assumes that at a given age (or duration since the start of a life) the force of mortality is a constant (specific to that age) multiplied by a proportionality factor which is determined by the characteristics of the individual and does not change unless these covariates do. In this paper, the method is reviewed for the case where the covariates are fixed at the start of the lifetime and illustrated by an application to marital dissolution in the United States.