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PubMed1995

Comparing standardized mortality ratios.

It is well known that the ratio of two standardized mortality ratios (SMRs) is not in general an unbiased estimate of the underlying within-stratum ratio of rates of one subcohort relative to another. It is also established, although less well known, that a sufficient condition for unbiasedness is that the underlying stratum-specific rates in each of the two subcohorts be proportional to the reference population. Further, the ratio of SMRs is more precise than the wholly internal (Poisson regression) estimate of rate ratio. In data that are compatible with the proportionality assumption, use of the ratio of SMRs thus buys precision at the cost of increased vulnerability to bias. To further elucidate choice between methods, we derive expressions for the asymptotic precision of each. These show that improved precision of ratio of SMRs depends on the extent to which the distribution of expected deaths over strata is different in the two cohorts, or equivalently, on the variance over strata of the proportion of expected deaths falling in the first cohort. The results are illustrated by hypothetic examples.

Bias↗
PubMed2004

The public and effective risk communication.

Public perceptions of risk have often been dismissed on the basis of "irrationality", and have tended to be excluded from policy processes by risk assessors and managers. People's responses to different risks are determined by psychological factors. The technical risk estimates traditionally provided by experts do not influence people's behaviours and responses in the same way as their risk perceptions. Some concerns are very specific to particular hazard. It is also important to communicate the difference between probability and variability associated with risk estimates. Risk communication must take account of the actual concerns of the public (for example, potential for negative environmental impact, unintended human health effects, or vulnerable groups within the population). When the public want information about a risk, they prefer a clear message regarding risks and associated uncertainties, including the nature and extent of disagreements between different experts. Furthermore, societal priorities for risk mitigation activities may not align with those identified by expert groups. Dismissing the former as irrelevant may result increased distrust in the motives of regulators and industry, with consequences for public confidence in regulatory activities linked to public protection. Awareness and understanding of public concerns must be the basis of an effective risk management strategy.

Communication↗
PubMed1992

Sterilization needs in the 1990s: the case for quinacrine nonsurgical female sterilization.

Much evidence suggests that demand for sterilization is a function of supply of surgical sterilization services in less-developed countries. If such services were greatly expanded, the number of procedures performed would grow dramatically. While the prevalence of sterilization is estimated to increase from 23.5% to 28.8% of married women of reproductive age in the 1990s, there will actually be 106,432,000 more couples of reproductive age at the end of this decade than at its beginning who use either no method or a far less effective method with much lower continuation rates than sterilization--nearly a 20% increase. To achieve a mean sterilization prevalence of 47% of married women of reproductive age in the less-developed world, as now seen in the Republic of Korea and Puerto Rico, the number of sterilizations would need to be more than double the current projection for the 1990s: 328,429,000 rather than 159,000,000. The quinacrine pellet method for nonsurgical female sterilization offers hope that this enormous shortfall in sterilization services can be overcome in this decade.

Adult↗
PubMed1998

New estimates of the effectiveness of the Yuzpe regimen of emergency contraception.

The purpose of this study was to provide new estimates of the effectiveness of the Yuzpe method of emergency contraception and to offer correctly computed estimates of the confidence intervals for estimated effectiveness rates. Through a literature search, seven studies that present the number of women treated and outcome of treatment by cycle day of unprotected intercourse relative to expected day of ovulation were identified. Probabilities of conception by cycle day of intercourse among women not using contraception and the associated variance-covariance matrix from five other datasets were estimated, and these external estimates were used to assess the effectiveness of the Yuzpe regimen. The 40 estimates of effectiveness, based on seven separate studies and the seven studies combined and five different sets of conception probabilities by cycle day, ranged from a low of 44.2% to a high of 88.7%. The preferred point estimate is that emergency contraceptive pills reduce the risk of pregnancy by 75.4%, with a 95% confidence interval extending from 65.6% to 82.4%. True effectiveness is likely to be at least 75% because treatment failures (observed pregnancies) include women who were already pregnant when treated and women who became pregnant after being treated.

Coitus↗
PubMed1998

A scenario study of oral contraceptive use in Japan. Toward fewer unintended pregnancies.

A scenario study was conducted to assess the extent to which the unintended pregnancy rate in Japan, where oral contraceptives (OC) have not been legalized for family planning purposes and couples rely mainly on condoms, might change if more women were to use OC. Because current rates of unintended pregnancy and abortion in Japan are not known, data provided by the 1994 Japanese National Survey on Family Planning were used to construct scenarios for national contraceptive use. Annual failure rates of contraceptive methods and nonuse were applied to the contraceptive use scenarios, to obtain estimates of the annual number of contraceptive failure-related pregnancies. Subsequently, contraceptive practice situations assuming higher OC use rates were defined, and the associated change in the number of contraceptive failure-related pregnancies was estimated for each situation. It emerged that OC use rates of 15% decreased the expected number of unintended pregnancies by 13%-17%, whereas use rates of 25% resulted in decreases of 22%-29% and use rates of 50% in decreases of 45%-58%. The findings were reasonably robust to variation in the assumptions that were made. In conclusion, each theoretical percentage increase in the OC use rate in Japan was found to lead to a roughly equivalent percentage decrease in the number of unintended pregnancies.

Adolescent↗
PubMed1998

Emergency contraception use and the evaluation of barrier contraceptives. New challenges for study design, implementation, and analysis.

The availability of emergency contraception (EC) introduces new complexities to barrier contraceptive evaluation. Researchers must determine whether the primary objective of interest is to measure the effectiveness of the barrier plus EC back-up or the effectiveness of the barrier alone. Barrier contraceptive effectiveness study protocols must specify what study volunteers will be told about EC, under what conditions EC will be dispensed, what information about EC use will be collected, and how EC use will be addressed during data analysis.

Contraception↗
PubMed1997

Longevity and life expectancy.

"In this article the evolution of life expectancy is examined historically for various European nations at various ages, and according to sex. Appropriate logistic equations describe the facts and extrapolate into the future giving the doctor an indication of what is still to be accomplished and the demographer the tools with which to evaluate the aging of European population in the next 20 years....I posit that the increase in life expectancy is the product of a learning process to remove the accidents and obstacles on the way to the full life potential of an individual: longevity."

Age Factors↗
PubMed1984

Forecasting first births.

This study is concerned with one aspect of the family cycle, namely, the transition from young married to young married with small children. The focus is on developing models to forecast entries into this latter stage for the purpose of marketing research. "Using ordinary least squares, forecasting models were estimated for (1) total number of first births, (2) number of white first births, and (3) number of nonwhite first births." Models are estimated for both the United States and California using data from official sources.

Black or African American↗
PubMed1989

Apartheid and AIDS.

Explore the source record for details and available documents.

Acquired Immunodeficiency Syndrome↗
PubMed1998

Estimation of megacity growth: simple rules versus complex phenomena.

"The growth of large urban aggregates (megacities) is analogous to the development of self-organized structures known in physics. Using empirical data about changes in the built-up areas of different cities as input, the self-organizing model employed here suggests that megacities evolve towards a hierarchical form of spatial organization, and provides estimates of the size of subclusters that compose the urban aggregate.... The model has been validated by reproducing the evolution of the Berlin area over a period of 35 years (1910-45). Using the same assumptions, the evolution of the built-up area of Daegu (Korea) is simulated up to the year 2010."

Asia↗
PubMed1997

Occupational change, employer change, internal migration, and earnings.

"In this paper I use microdata from the [U.S.] Panel Study of Income Dynamics to measure the financial returns to intercounty and interstate migration for individuals in a temporal framework accounting for gains that accrue over time.... To account for the indirect effects of migration on earnings, explanatory variables are created by interacting migration status with: (1) occupational change, (2) employer change and (3) changes in both occupation and employer. These interaction terms are then included in the earnings functions. Earnings are estimated for three years subsequent to the migration decision to account for the financial returns to migration accruing over time. Results indicate that, when estimating earnings, the use of a simple migration dummy variable will mask the indirect effects of migration on earnings."

Americas↗
PubMed1997

Further thoughts on simplicity and complexity in population projection models.

"This article is a review of--and response to--a special issue of Mathematical Population Studies that focused on the relative performance of simpler vs. more complex population projection models. I do not attempt to summarize or comment on each of the articles in the special issue, but rather present an additional perspective on several points: definitions of simplicity and complexity, empirical evidence regarding population forecast accuracy, the costs and benefits of disaggregation, the potential benefits of combining forecasts, criteria for evaluating projection models, and issues of economic efficiency in the production of population projections."

Cost-Benefit Analysis↗
PubMed1998

Combining probabilistic and subjective assessments of error to provide realistic appraisals of demographic forecast uncertainty: Alho's approach.

"With increasing interest in forecast uncertainty, there is an evolving concern with assessing the degree of certainty we can attach to uncertainty itself. This concern is the subject of recent work by Juha Alho.... I examine [his] approach systematically and draw general conclusions about its efficacy. Suggestions for improvement are made."

Evaluation Studies as Topic↗
PubMed1998

Migration, self-selection and earnings in Philippine rural communities.

"Estimated returns to schooling investments can be misleading if migration causes significant shifts in population distribution across time. Data gathered in rural Philippine communities show that the more educated and experienced individuals are more likely to outmigrate, causing a sample selection bias in the estimation of wage equations. The observed wages were then lower than the conditional population mean of an entire cohort residing originally in the area. Controlling for self-selection, the wage returns to schooling and experience were higher, Finally, the sample selectivity variable accounts substantially for the difference in the wages of men and women."

Asia↗
PubMed1999

Stratified partial likelihood estimation.

When multiple durations are generated by a single unit, they may be related in a way that is not fully captured by the regressors. The omitted unit-specific variables might vary over the durations. They might also be correlated with the variables in the regression component. The authors propose an estimator that responds to these concerns and develop a specification test for detecting unobserved unit-specific effects. Data from Malaysia reveal that concentration of child mortality in some families is imperfectly explained by observed explanatory variables, and that failure to control for unobserved heterogeneity seriously biases the parameter estimates.

Asia↗
PubMed1999

Discrete factor approximations in simultaneous equation models: estimating the impact of a dummy endogenous variable on a continuous outcome.

This paper contains a Monte Carlo evaluation of estimators used to control for endogeneity of dummy explanatory variables in continuous outcome regression models. When the true model has bivariate normal disturbances, estimators using discrete factor approximations compare favorably to efficient estimators in terms of precision and bias; these approximation estimators dominate all the other estimators examined when the disturbances are non-normal. The experiments also indicate that one should liberally add points of support to the discrete factor distribution. The paper concludes with an application of the discrete factor approximation to the estimation of the impact of marriage on wages.

Economics↗
PubMed1997

Documented homicides and excess deaths: new insights into the scale of killing in the USSR during the 1930s.

"Getty, Rittersporn and Zemskov recently claimed that no more than 2 million people could have perished from collectivization, famine, execution, terror, and forced labor in the USSR during the 1930s. Prior demographic confirmation of this estimate was provided by Anderson and Silver who contended that killings were unlikely to exceed a few million and could not be more than 4.8 million victims. This essay disproves both these contentions by introducing new demographic evidence proving that Stalin killed at least 5.2 million Soviet citizens 1927-1938, with a best estimate in the vicinity of 10 million."

Cause of Death↗