ISSN:0277-6715    

DOI:10.1002/sim.4780100202

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractIn the transition from high to low fertility, different biological and behavioural proximate determinants play roles of varying importance in mediating the change. In most regions of the world, the practice of contraception has come to play the major role, so much so that there is a close relationship worldwide between the level of practice of contraception and the level of fertility. In sub‐Saharan Africa, the prevalence of contraceptive practice is low, and fertility levels are exceptionally high for recorded levels of contraceptive practice, even where levels of contraceptive practice are comparable to other regions. The discrepancies are explained to a very large extent by differences between Africa and other regions in other proximate determinants‐notably exposure to the risk of pregnancy, and abstinence after delivery. It would seem that transition in African countries will follow one of two patterns that are different to the pattern of transition observed in all other regions. First, fertility may rise before it declines, due to abandonment of traditional fertility regulation for some time prior to the eventual adoption of contraceptive practice. Second, the prevalence of contraceptive practice may rise for a time before there is an observable decline in fertility, because at the same time that contraception is adopted, traditional regulation of fertility is being abandoned, offsetting any effect on fertility. Kenya is an example of the first pattern, while Botswana, Ghana, and Zimbabwe are probably examples of the sec

ISSN:0277-6715    

DOI:10.1002/sim.4780100203

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractSince the mid 1970s, the World Health Organization's Special Programme of Research, Development and Research Training in Human Reproduction, through its Task Force on Vaccines for Fertility Regulation, has been supporting and coordinating the development of a birth control vaccine based on a synthetic peptide representing part of the beta subunit of human chorionic gonadotrophin (β‐hCG). The majority of this work has been carried out in the laboratories of Dr V. C. Stevens at Ohio State University. This hCG vaccine has recently been tested for tolerability and immunogenicity in a phase I clinical trial, and a preliminary evaluation of the vaccine's efficacy in fertile women volunteers is currently being planned. This paper describes the preclinical and clinical testing of this vaccine and the problems and challenges presented by this novel preparation. These have included the need to carry out safety and efficacy studies in the baboon, and the difficulties of designing appropriate preclinical toxicity and immunosafety studies and clinical trial protocols in the absence of previous experience with vaccines of this ty

ISSN:0277-6715    

DOI:10.1002/sim.4780100204

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractMisreporting of dates and ages poses serious difficulties for the estimation of the age distribution and birth and death rates in many developing countries. The pervasiveness of these problems is illustrated with data from a well‐designed on‐going survey in Pakistan, the Pakistan Demographic Survey. Methods for reconciling discrepancies, based on the assumptions of constant misreporting and survivorship patterns, are presented. The reasoning behind these methods could be applied much more generally. Research into the cultural interpretations of age and dates, and the nature of possible biases, is called

ISSN:0277-6715    

DOI:10.1002/sim.4780100205

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractAlthough the literature on contraceptive failure is vast and is expanding rapidly, our understanding of the relative efficacy of methods is quite limited because of defects in the research design and in the analytical tools used by investigators. Errors in the literature range from simple arithmetical mistakes to outright fraud. In many studies the proportion of the original sample lost to follow‐up is so large that the published results have little meaning. Investigators do not routinely use life table techniques to control for duration of exposure; many employ the Pearl index, which suffers from the same problem as does the crude death rate as a measure of mortality. Investigators routinely calculate ‘method’ failure rates by eliminating ‘user’ failures from the numerator (pregnancies) but fail to eliminate ‘imperfect’ use from the denominator (exposure); as a consequence, these ‘method’ rates are biased downward. This paper explores these and other common biases that snare investigators and establishes methodological guidelines fo

ISSN:0277-6715    

DOI:10.1002/sim.4780100206

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractThe identification of the human fertile phase as the time during which a woman or a couple may conceive is elusive. The fertile time depends on many factors in each individual menstrual cycle and may be said to be more of a statistical than a physiological entity. This paper reviews the application of statistical methods to three areas related to conception and the fertile phase. The first is the prediction and detection of ovulation from serial measurements, such as hormones, basal body temperature and cervical mucus, throughout the menstrual cycle. Typically, such variables increase from some baseline level to a peak around ovulation (the most fertile time), then subside to low levels in the postovulatory phase. The statistical challenge is to detect the rise (signalling the onset of potential fertility) and subsequent fall. Analytic methods considered include thresholds, Bayesian change‐point models and particularly the cumulative sum (cusum) technique which is both simple to apply and understand, and effective. The second area comprises appropriate methods of analysing and interpreting data from clinical studies of the fertile phase, especially in so‐alled natural family planning (NFP) where it is usual for women to observe several indices of potential fertility. Such studies usually try to establish the temporal relationships between markers of the fertile phase and examine the success of different combinations of markers in delineating the fertile time in comparison with a standard ‘defined’ phase, for example, the interval from three days before to two days after the peak of luteinizing hormone. The third area is the assessment of the probability of conception on certain days of the cycle, which is vital to the understanding of the fertile phase and its application to NFP. Direct estimation of such probabilities is impractical; instead, resort must be made to estimation by maximum likelihood of the parameters of specially constructed models. Suitable models are described. Finally, the need for a new prospective study of the probability of conception in relation to the markers of the fertile phase used in the symptothermal method of NFP is di

ISSN:0277-6715    

DOI:10.1002/sim.4780100207

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractThe vaginal ring is one method of contraception currently under investigation and development by the Human Reproduction Programme of WHO. One factor that reduces its acceptability is that some women experience involuntary expulsions of the ring. WHO have collected prospective data on 1005 women from 19 centres worldwide to investigate various aspects of ring use including factors that might affect expulsions. For each subject the data include number of expulsions, age, parity, ponderal index, number of days of ring use and health care centre. To model the factors influencing expulsion, the number of expulsions was first considered as a Poisson variate with mean directly proportional to the log of the duration of ring use. Such a model gave a poor description of the data and it appeared that the number of expulsions was considerably over‐dispersed for an assumed Poisson variate. This paper examines a variety of strategies for coping with the resulting lack of fit of the model. It turns out that a truncated Poisson model gives a better description of the expulsion data and that health care centre and parity influence the rate

ISSN:0277-6715    

DOI:10.1002/sim.4780100208

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractWe have developed a method of estimating day of ovulation using urinary ovarian hormone data. The method identifies a day of luteal transition that occurs at the shift from production of follicular oestrogen to luteal progesterone. The algorithm for identifying this shift was evaluated and judged better than specified alternatives in that it resulted in (1) a high concordance between the day of luteal transition and peaks in urinary luteinizing hormone (LH) for cycles with well‐defined peaks, (2) a low variance in the length of the luteal phase of the menstrual cycle, which presumably reflects a low measurement error in estimating day of ovulation, and (3) a high proportion of cycles for which an approximate day of ovulation could be determined. To validate the new algorithm, it was applied to an independent data set. The algorithm identified a day of luteal transition in 88 percent of these cycles, and the identified day occurred within two days of the urinary LH peak for all of the cycles with clear LH peaks. Determination of the day of luteal transition to estimate ovulation requires only first‐morning urine specimens, requires no correction for day‐to‐day variations in urine concentration, and can be applied to a mid‐ycle windo

ISSN:0277-6715    

DOI:10.1002/sim.4780100209

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractThe disturbance in menstrual bleeding induced by many methods of contraception is an important factor in their acceptability, and women participating in clinical trials of new methods are usually asked to keep a calendar record of the occurrence of bleeding. A recent WHO report recommends that, for analysis and presentation, each menstrual diary should be divided into successive periods, and the woman's bleeding pattern in each period summarized in ten indices. These indices are simple to calculate and easily understood by clinicians, but comparison of several groups is problematic because of the large number of summary statistics generated.Principal components analysis was therefore used to determine whether the indices could be reduced to a smaller number of measures. The analyses showed that three of the indices ‐ the range and maximum value of bleeding/spotting episode lengths and the minimum bleeding‐free interval ‐ rarely measure their intended dimension of the bleeding pattern. Most of the essential information about a woman's bleeding pattern is contained in only four of the ten indices: the number of bleeding/spotting episodes, the mean lengths of episodes and intervals, and the range of bleeding‐free interval lengths. Together, these indices describe the most important dimensions of a pattern: the amount, frequency and variability of the b

ISSN:0277-6715    

DOI:10.1002/sim.4780100210

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractWe propose a method of estimating the miscarriage risk in a setting where counts of births, miscarriages and induced abortions are available, and also the gestational week of each induced abortion. Unlike previously proposed methods, ours takes into account the fraction of the miscarriage risk to which each interrupted pregnancy has been exposed. For this purpose, we draw on an extraneous standard foetal survival curve and stipulate that the survival curve of the study population is a scaled version thereof. Three such scaling models are discussed, and it is shown that the choice is largely a matter of computational convenience. Separate attention is given to a competing‐risk model of miscarriages and interruptions, and examples are given of reasons why the crucial assumption that these two sources of termination operate independently is unlikely to be met. Finally, it is argued that pregnancy wishes, especially those of habitual aborters, shape the miscarriage rate to the extent that it becomes as much a cultural parameter as a marker of biological hazard

ISSN:0277-6715    

DOI:10.1002/sim.4780100211

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY