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At least 955 records · Page 53Linked to original sources
PubMed1994

Preparation for phase III HIV vaccine efficacy trials: methods for the determination of HIV incidence.

OBJECTIVE: Accurate estimates of HIV incidence that reflect the effect of non-vaccine interventions (education, counselling, condom promotion, and possibly sexually transmitted disease treatment) and that may be provided in a Phase III vaccine efficacy trial, are needed so that vaccine trial population sample sizes can be accurately determined. In order to avoid delays in the implementation of efficacy trials, well characterized cohorts must also be developed and available to participate in such trials. We reviewed the potential study populations, the epidemiologic methods for the determination of HIV incidence (using open cohort, closed cohort, and seroprevalence data methods), and the need for the development of population cohorts in preparation for Phase III HIV vaccine efficacy trials. SETTING: Phase III trials in developed and developing countries. METHODS: Comparison of open and closed cohorts and those using seroprevalence data to estimate HIV incidence. RESULTS: Open and closed cohorts each have disadvantages and advantages. However, the open cohort may be more suitable for determining estimates of HIV incidence that reflect non-vaccine interventions and for the development of a well characterized cohort available to participate in efficacy trials. CONCLUSION: Careful preparation of research infrastructures and population cohorts will help ensure the successful conduct of scientifically and ethically sound HIV vaccine efficacy trials in the future.

AIDS Vaccines↗
PubMed1996

Demographic approaches to the estimation of incidence of HIV-1 infection among adults from age-specific prevalence data in stable endemic conditions.

OBJECTIVE: To develop methods for estimating the incidence of HIV-1 infection among adults from age-specific prevalence data derived in stable endemic conditions. METHODS: Two methods are proposed. The first method is the Cumulative Incidence and Survival Method which treats HIV-1 prevalence at any given age as the cumulative incidence of new infections at each preceding age, adjusted for mortality. A model for age-specific incidence is fitted to the data using maximum likelihood techniques. The other method is the Constant Prevalence Method whereby the incidence of new infections within a time interval (t-r, t) is calculated as the difference, after adjusting for mortality, between observed prevalence levels at two successive age intervals, whose mean ages are r years apart. The two methods were applied to data from Kampala, Uganda. RESULTS: Plausible estimates of age-specific and cumulative HIV-1 incidence were obtained from each of the methods. Estimates of HIV-1 incidence are sensitive to assumptions regarding the length of the survival period after infection and the stability of the epidemic. CONCLUSIONS: Reasonable estimates of HIV-1 incidence can be obtained from prevalence data derived in near-stable conditions. With the Constant Prevalence Method, these conditions may be relaxed if large sample sizes are available and age-reporting is good. The methods proposed could be used in the design and implementation of HIV-1 prevention trials. Cumulative incidence is a better indication of demographic impact than average age-specific incidence.

Adult↗
PubMed1998

Reproducibility of cardiovascular, respiratory, and metabolic responses to submaximal exercise: the HERITAGE Family Study.

This study determined the reproducibility of cardiovascular, respiratory, and metabolic responses to submaximal cycle ergometer exercise at two power outputs (50 W and 60% VO2max) on each of two separate days in a sample of 390 subjects (198 men and 192 women) participating in the HERITAGE Family Study. The same protocol was conducted across 3 d in an intracenter quality control substudy which included an additional 55 subjects. Reproducibility estimates included technical error, coefficient of variation, and intraclass correlation for each of the selected variables for both subject populations. Further, since the data were collected across four clinical centers, intraclass correlations were also computed separately by clinical center. Most variables were highly reproducible, with coefficients of variation below 9% and intraclass correlations over 0.80. These results were consistent for both subject populations and across all four clinical centers. Reproducibility indicators were generally better at the higher power output. It is concluded that within-subject day-to-day variation and measurement unreliabilities are generally small compared with the between-subject variance in the response to submaximal exercise at each of the clinical centers of the HERITAGE Family Study.

Adolescent↗
PubMedDate not supplied

Estimating the effective rate of sex partner change from individuals with sexually transmitted diseases.

BACKGROUND AND OBJECTIVES: The effective rate of partner change is an important variable for determining whether an epidemic of a sexually transmitted disease (STD) occurs. It is essential for understanding the transmission dynamics of STDs. GOAL OF THIS STUDY: The problem of estimating the effective rate of partner change is addressed. RESULTS: Under certain conditions the mean rate of partner change in STD patients estimates the effective rate of partner change in the general population. CONCLUSION: To estimate the effective rate of partner change in a population, the use of surveys of patients with STD provides a simpler and less costly alternative to population surveys of sexual behavior.

Bias↗
PubMed1999

Current estimates of and future projections for adult deaths attributed to HIV infection in Zimbabwe.

OBJECTIVE: Estimates of HIV prevalence in 1995 among all adults in Zimbabwe range between about 18% and 24%. The objective of this study was to estimate, for Zimbabwe, the impact of HIV infection on adult mortality, by age and gender, between 1995 and the year 2000. METHODS: For this analysis, we used 1992 census data to estimate the number of non-HIV-related deaths, and a short-term projection model to estimate the number of deaths attributed to HIV infection in 1995 and the year 2000. RESULTS: It was estimated that between 52% and 60% of all adult deaths in 1995 were attributed to HIV infection, and between 69% and 76% in both males and females in the group between 20 and 39 years of age. The estimated adult mortality rate per 1000 increased from 9.8 in 1987 (based on census data) to between 20.6 and 24.3 in 1995. For the year 2000, it was projected that between 66% and 73% of all adult deaths would be attributed to HIV infection, and between 81% and 86% in those aged 20 to 39 years. The estimated adult mortality rate in the year 2000 increased to between 29.1/1000 and 36.6/1000. Even if all transmission was assumed to cease after 1995, it was projected that >60% of adult deaths would be attributed to HIV in the year 2000. Adult population growth is projected to decrease to between 0.3% and 1.0% in the year 2000. CONCLUSION: Results suggest that the impact of HIV infection on mortality in Zimbabwe is already severe and will continue to increase. Efforts to reduce numbers of new HIV infections today will serve to reduce the future burden of mortality, particularly in the longer term.

Adolescent↗
PubMed1992

Age-dependent choice of sexual partners and the transmission dynamics of HIV in Sub-Saharan Africa.

A mathematical model of the transmission of HIV-1 within heterosexual populations in Sub-Saharan Africa is described and its properties analysed. The model incorporates epidemiological and demographic processes and extends previous work in this area via the inclusion of age and sex dependency in rates of sexual partner change, and sexual partner choice dependent on age. Parameter assignments are made on the basis of current data on the transmission dynamics of HIV-1 and the demography of human populations in Africa. Both age-dependent rates of sexual activity and the sexual contact of males with females younger than themselves act to enhance the predicted demographic impact. With realistic parameter values, the model suggests AIDS is able to reverse the sign of population growth rates from positive to negative values over a timescale of a few decades. The sensitivity of this prediction is examined in relation to changes in the pattern of sexual contact between different age classes of females and males, different patterns of change in the age-dependent rate of sexual partner change, different assumptions concerning the doubling time of the epidemic in its early stages, and the relative efficiencies of viral transmission between men and women, and vice versa. The impact AIDS is predicted to have on the number of young and elderly persons as a fraction of the number of productive adults (the dependancy ratio) is examined under various assumptions concerning the weighting to be applied to mirror the burden imposed by the care of those with AIDS. The paper includes an assessment of the influence of the timing of changes in sexual behaviour, or the promotion of the use of condoms, on the predicted course of the epidemic. The paper concludes with a discussion of data needs and the model refinements required to more accurately mirror current understanding of the epidemiology of HIV-1.

Acquired Immunodeficiency Syndrome↗
PubMed1997

Scenarios, uncertainty and conditional forecasts of the world population.

This study is concerned with the methods available for the forecasting of future trends in the world's population. Particular attention is given to the problem of the uncertainties that these forecasts include. "The purpose of this paper is to show how subjective and data-based probabilistic assessments of error can be combined, to give a user a realistic assessment of the uncertainty of demographic forecasts, and to apply these concepts to forecasts of the world population. Moreover, we shall show how conditional forecasts can provide a simple conceptual framework in which to view scenarios. They can be particularly useful in the evaluation of proposed policies. Indeed, the so-called environmental impact assessments...that are now mandatory in many countries for major construction projects typically contain elements of conditional forecasting." The concepts discussed are illustrated by comparing a scenario of future global population growth prepared at the Institute of Applied Systems Analysis with a UN population projection.

Forecasting↗
PubMed1999

The long-term pattern of adult mortality and the highest attained age.

"Recent new data on old age mortality point to a particular model for the way in which the probability of dying increases with age. The model is found to fit not only modern data but also some widely spaced historical data for the 19th and 17th centuries, and even some estimates for the early mediaeval period. The results show a pattern which calls for explanation. The model can also be used to predict a probability distribution for the highest age which will be attained in given circumstances. The results are relevant to the current debate about whether there is a fixed upper limit to the length of human life." A discussion of the paper by several researchers and a reply by the author are included.

Age Distribution↗
PubMed1999

A methodological strategy for a one-number census in the UK.

"As a result of lessons learnt from the 1991 [U.K.] census, a research programme was set up to seek improvements in census methodology. Underenumeration has been placed top of the agenda in this programme, and every effort is being made to achieve as high a coverage as possible in the 2001 census. In recognition, however, that 100% coverage will never be achieved, the one-number census (ONC) project was established to measure the degree of underenumeration in the 2001 census and, if possible, to adjust fully the outputs from the census for that undercount. A key component of this adjustment process is a census coverage survey (CCS). This paper presents an overview of the ONC project, focusing on the design and analysis methodology for the CCS. It also presents results that allow the reader to evaluate the robustness of this methodology."

Censuses↗
PubMed1992

Population trends, issues and implications.

"The aim of the paper is to provide an overview of the population trends in Africa, the critical population issues of the region and their implications, as well as linkages with important social and economic sectors such as education, health, employment, food and nutrition etc. The time frame for the paper is the recent past and the immediate future until 2025 for which United Nations projections are available. The data utilized in the paper are the United Nations Population Projections as assessed in 1988 supplemented by information available from various surveys and studies, particularly the World Fertility Surveys and Demographic and Health Surveys."

Africa↗
PubMed1996

Continuing demographic transitions in Asia.

"This article updates the literature survey on demographic trends and policies published in the May 1987 issue of this journal. It reports substantial adjustments in earlier population projections, suggesting slower decline in population growth rates for China and several other Asian countries. It gives an account of recent trends and policies in the Asian-Pacific region, especially China, Vietnam, Indonesia, the Philippines and Singapore."

Asia↗
PubMed1981

On estimating internal migration for open populations.

"The purpose of this note is to review the case for using the forward census survival ratio (FCSR) method for estimating internal migration. Through this technique seems likely, on certain criteria, to offer usable estimates of migration, it suffers from what some critics regard as a crucial weakness, namely a sensitivity to inernational migration. It is argued here, however, that this deficiency is less damaging than others have made it out to be. Consequently, a case can be made for preferring the FCSR method to other methods."

Demography↗
PubMed1984

Regional economic-demographic modelling and projection: review of an international conference.

A review of the papers presented at the International Conference on Forecasting Regional Population Change and Its Economic Determinants and Consequences, held at Airlie House, Virginia, from May 26 to 29, 1982, is provided. "This review...concludes that [regional economic-demographic] modelling is at an early stage of development and currently provides only an adjunct to more conventional methods of regional forecasting. Given expected future improvements in the theory, data and techniques of economic-demographic modelling, such models could soon provide a worthwhile alternative."

Congresses as Topic↗