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PubMed2003

Life table characteristics of Anopheles arabiensis (Diptera: Culicidae) under simulated seasonal conditions.

Life tables provide a summary of mortality and reproductive schedules and can help explain why certain species proliferate in particular environments. Life table characteristics of Alopheles arabiensis, under a range of simulated seasonal temperature were determined. F1 progeny of field-collected material were observed at four fluctuating temperatures with means of 17.9, 23.2, 26.1, and 21.4 degrees C, representing winter, spring, summer and autumn temperature profiles. Gonotrophic cycles, egg hatchability rates, mean male and female lifespans, reproductive rate, the intrinsic rate of increase, and generation times were calculated. Immature development was fastest in summer (11 d) compared with winter (32 d), resulting in less robust adults. Mean female lifespans were greater than those of the males and also increased with decreasing temperatures. From the age-specific survivorship curve and the gonotrophic cycles, females were found to lay large numbers of eggs especially during spring and summser. Under simulated winter conditions mosquitoes did not oviposit in the laboratory. It was also determined that summer reared mosquitoes are capable of giving just one infected bite while autumn reared mosquitoes can give two infected bites, increasing their transmission potential. Thus life table data go some way toward explaining late season transmission of malaria in South Africa.

Animals↗
PubMed2005

Life expectancy--a commentary on this life table variable.

In 1992, I wrote an article on a method of modifying the Decennial US Life Table to accommodate any pattern of excess mortality expressed in terms of excess death rate (EDR), for the specific purpose of calculating the reduced life expectancy, e. I believe this was the first article published in the Journal of Insurance Medicine (JIM) that dealt specifically with life expectancy as an index of survival and risk appraisal, never used in the classification of extra mortality risk in applicants for life insurance. In this commentary, I discuss the 1989-91 US Decennial Life Table in detail. I link the subject matter of the 1992 article with several more recent articles that also focus on the utility of life expectancy in underwriting structured settlement annuities and preparing reports on life expectancy for an attorney in a tort case. A few references are given for further reading on life table methodology and its use in the most accurate estimate of life expectancy, given the inherent limitations of the life table and the limited duration of follow-up studies.

Adolescent↗
PubMed1988

The parameters of death: a consideration of the quantity of information in a life table using a polynomial representation of the survivorship curve.

How much unique information is contained in any life table? The logarithmic survivorship (lx) columns of 360 empirical life tables were fitted by a weighted fifth degree polynomial, and it is shown that six parameters are adequate to reproduce these curves almost flawlessly. However, these parameters are highly intercorrelated, so that a two-dimensional representation would be adequate to express the similarities and differences among life tables. It is thus concluded that a life table contains but two unique pieces of information, these being the level of mortality in the population which it represents, and the relative shape of the underlying mortality curve.

Actuarial Analysis↗
PubMedDate not supplied

Calculation of actuarial life tables with use of a microcomputer spreadsheet program.

PURPOSE: To simplify the calculation of the life-table method of survival analysis. MATERIALS AND METHODS: A template was developed for use with a popular microcomputer spreadsheet program to perform life-table survival calculations and to perform statistical comparisons between the survivals of groups of patients with use of the log-rank test. RESULTS: The template successfully performed life-table and log-rank calculations when compared with two standard, accepted statistical computing programs. CONCLUSION: The template can be used to quickly perform life-table calculations that can be used in the long-term follow-up of patients undergoing interventional radiologic procedures.

Female↗
PubMed1978

Calculating life tables by estimating Chiang's a from observed rates.

A simple, accurate method of life table construction is advanced based upon a new way to estimate Chiang's nax (the average number of years lived in the x to x + n age interval by those dying in the interval). The estimate for nax leads immediately to an expression for lx+n (the survivors to age x + n) in terms of lx and the known mortality rates for the interval x to x+n and the two adjacent intervals. The complete solution for the basic life table is given. The proposed method and five other easily applied methods are then compared against the standard provided by the U.S. life tables for 1969-1971. The results attest to the excellent performance and high degree of accuracy of the proposed method. Finally, extensions of the method to multiple decrement and associated single decrement life tables are briefly described.

Humans↗
PubMed1987

Extension of life-table methodology to allow for left-censoring in survival studies of pacing devices followed by commercial monitoring services.

The actuarial life-table is commonly used to describe lifetime data of living subjects and manufactured products. The life-table method allows subjects to come under observation at different times and, thus, to have differing lengths of follow-up, by assuming all subjects begin their lifetimes relative to the outcome of interest at some common point in time. As time progresses, subjects are withdrawn from the life-table when their period of observation has elapsed. This pattern of follow-up is often termed "right-censoring." An important feature of the classical life table approach is that the time at which the subject is placed at risk is known, and the status relative to the outcome of interest is known for the entire time at risk. Sometimes, however, subjects cannot be observed for some period after the beginning of their lifetimes. The example to be considered involves follow-up data collected by a commercial pacemaker monitoring service, to which patients subscribe, generally at some point following the actual implant of the pacemaker. Since the outcome of interest is device failure after implant, some means of dealing with the lack of information between implant and initiation of follow-up is needed. The extension of the actuarial life-table to accommodate this "left-censoring" will be described in this paper.

Actuarial Analysis↗
PubMed1982

A modified life table method to study congenital genetic disorders: an application in sickle cell anemia.

A modified life table procedure is introduced designed to study the survival of patients with congenital genetic disorders with the endpoint defined by a complication or death. It uses the ages of the patients as the time axis as in "population' or "current' life tables, and it allows patients to enter and exit the study as in survival life tables. The procedure uses the exact length of time that each patient is observed in the study to determine the conditional probabilities of developing the complication. The proposed procedure is especially helpful in studying recurrent complications or events that occur frequently. The proposed life table procedure is demonstrated in the study of the conditional probability of developing a sickle cell crisis in 509 patients with sickle cell anemia (SS) with different number of prior crises. The demonstration is intended to illustrate the use of the proposed method and not to investigate the clinical severity of sickle cell anemia. It was found that the risk of crisis was to investigate the clinical severity of sickle cell anemia. It was found that the risk of crisis was positively related to the number of prior crises in SS patients (P less than 0.001). This trend was significant in the first three decades of life.

Actuarial Analysis↗
PubMed1985

Actuarial contributions to life table analysis.

The correct principles for the construction of life tables and more particularly select life tables were developed by actuaries in England in the first half of the 19th century. Actuaries explored the phenomenon of selection not only between the insured and annuitants but also in the general population, distinguishing among initial temporary selection, antiselection, and class selection. The conclusion was reached early that no such thing as an unselected population exists. Group life insurance experience among the actively employed has been shown to provide a more appropriate standard of expected mortality than general population death rates in studies of medical impairments and occupational hazards at ages under 65 years. Mortality rates derived from the Cancer Prevention Study can serve as a useful standard of expected mortality when the objective is determination of excess mortality compared with ostensibly healthy persons at ages 65 years and older.

Actuarial Analysis↗
PubMed1990

A comparative study of the life tables of Assam, Kerala and India, 1980.

The authors construct "life tables for Assam...using the Sample Registration System data of 1980 [and applying] Greville's method of constructing abridged life tables. These tables are compared with those of Kerala and India. Brass' two parameter logit system [when] fitted to survivors shows that risk of mortality of Kerala females, is much lower than that of India and Assam."

Asia↗
PubMed1996

Extension of the life table to repeating and changing events.

Estimation of cumulative and adjusted occurrence of life events and measures over time is often important in settings where study subjects have incomplete or different follow-up periods. Well-known methods to do this, such as the life table and age adjustment, exist for binary nonrecurrent events (i.e., death). However, a general approach to evaluate recurrent life events (e.g., repeated infections), life events with different durations (e.g., hospitalization days), costs, or changing life measures (e.g., body weight) is not available. This paper develops the "Life-Event Table," an analog of the life table that can analyze occurrence of diverse types of events and measures when the observation periods of subjects are incomplete and different. This method, based on a central limit theorem for incomplete multivariate data, obtains point estimates and variances for cumulative incidence, age-adjusted expectation, and other quantities. Simple hypotheses tests and comparisons are possible with this approach. Three applications are presented. The Life-Event Table may facilitate use of currently available robust multivariate analysis methods. Further research into other multivariate methods that take advantage of this Life-Event Table's specific covariance/variance structure may be warranted.

AIDS-Related Opportunistic Infections↗
PubMed2005

On the construction of clinical life table for studying the survivability of diagnosed AIDS cases.

In this paper, an attempt has been made to estimate the various survival functions of clinically diagnosed AIDS cases by the life table method. The actuarial life table method has already been applied to clinical data for many decades. To exhibit computations for the clinical life table, we have used the clinical data gathered on diagnosed 731 male and female AIDS patients recorded from Dec.1993 up to Dec.2002 in Delhi. The method is also used to study the nature of the survival functions for the AIDS patients with different causes of death. The comparisons among various survival functions are shown with the help of the graphs.

Acquired Immunodeficiency Syndrome↗
PubMed1988

Mathematical hazard models of mortality: an alternative to model life tables.

A five-parameter competing hazard model of the age pattern of mortality is described, and methods of fitting it to survivorship, death rate, and age structure data are developed and presented. The methods are then applied to published life table and census data to construct life tables for a Late Woodland population, a Christian period Nubian population, and the Yanomama. The advantage of this approach over the use of model life tables is that the hazard model facilitates life-table construction without imposing a particular age pattern of mortality on the data. This development makes it possible to use anthropological data to extend the study of human variation in mortality patterns to small populations.

Adolescent↗
PubMed1977

Life-table analysis of IUDs: problems and recommendations.

Two major prospective studies of copper-bearing IUDs showed substantial changes in termination rates when calculated at different dates. One of the studies employed the Tietze life-table method and showed progressive increases in termination rates with the passage of time. The other study used the Potter life-table method and showed sharply decreased termination rates at later assessments. In investigating the reasons for these changes, it was noted that the data collected for periodic analyses during the studies violated the assumptions underlying the life-table technique. It was discovered that as a result of these violations the Potter and the Tietze life-table calculations based on the same set of data produced markedly different estimates of IUD termination rates during the course of a study. Underlying these differences, and the reason for the apparent changes in termination rates, was a large set of incomplete observations. Neither of the two life-table methods was able to deal adequately with the biases arising from these incomplete observations. The "anniversary method," devised to overcome the perceived problems of the Potter and Tietze methods, also proved inadequate to deal with the incomplete observations. Only vigorous and active follow-up, together with ample time to complete data collection, editing, coding, and key punching, is likely to reduce the proportion of women with incomplete observations and is likely to minimize the biases attendant upon incomplete or partial observations of acceptors in prospective clinical studies of IUDs.

Evaluation Studies as Topic↗
PubMed2000

Statistical inference on associated fertility life table parameters using jackknife technique: computational aspects.

Knowledge of population growth potential is crucial for studying population dynamics and for establishing management tactics for pest control. Estimation of population growth can be achieved with fertility life tables because they synthesize data on reproduction and mortality of a population. The five main parameters associated with a fertility life table are as follows: (1) the net reproductive rate (Ro), (2) the intrinsic rate of increase (rm), 3) the mean generation time (T), (4) the doubling time (Dt), and (5) the finite rate of increase (lambda). Jackknife and bootstrap techniques are used to calculate the variance of the rm estimate, which can be extended to the other parameters of life tables. Those methods are computer-intensive, their application requires the development of efficient algorithms, and their implementation is based on a programming language that encompasses quickness and reliability. The objectives of this article are to discuss statistical and computational aspects related to estimation of life table parameters and to present a SAS program that uses jackknife to estimate parameters for fertility life tables. The SAS program presented here allows the calculation of confidence intervals for all estimated parameters, as well as provides one-sided and two-sided t-tests to perform pairwise or multiple comparison between groups, with their respective P values.

Animals↗
PubMed1976

The life table. A method for analyzing longitudinal studies.

The life table is presented as the method of choice for analyzing data from longitudinal studies in which the outcome under study occurs randomly and in which patients are followed up varying lengths of time. We discuss the superiority of the life table to methods typically used, the calculation of its entries, and some of the clinical uses that can be made of its results. The method is applied to follow-up data on manic-depressive patients maintained with prophylactic lithium carbonate or with control regimens, and it is shown to disclose mathematical regularities in the parameters of longitudinal course.

Adult↗
PubMed1984

Life table construction on the basis of two enumerations of a closed population.

The author demonstrates that an accurate detailed life table that represents average mortality experience between two censuses can be constructed if the censuses provide accurate records of the single-year age distribution of a closed population. This life table can begin at age zero if accurate data on the annual number of births during the inter-censal period are available; otherwise the first age in the life table must equal the duration of time between the censuses. "The estimation technique involves the calculation of the number of persons attaining each age during the period between the censuses and the determination of the average rate of increase in the number at each individual age. The success of the technique comes from the use of interpolation to calculate how many in each cohort attain each exact age the cohort passes through between the censuses." The estimation technique is tested using two alternative methods of interpolation. Some illustrations based on data for Sweden and China are included.

Age Distribution↗