Fitting a logistic curve to population size data

A stochastic logistic process N(,t) is viewed as a homogeneous birth and death process with population birth and death rates (lamda)(,n) = (a(,1)-b(,1)n)n and (mu)(,n) = (a(,2)+b(,2)n)n, respectively, where a(,1), a(,2) \u3e 0, b(,1), b(,2) (GREATERTHEQ) 0, a(,1)(NOT=)a(,2), b(,1)+b(,2) \u3e 0, and n is the population size, a realization of N(,t);The mean value and the covariance function of the stochastic logistic growth were estimated using computer simulations. The stochastic mean at time t was found to be extremely close to the deterministic mean, K/(1+Ce(\u27-rt)), where r = a(,1)-a(,2) is the intrinsic individual growth rate, K = r/(b(,1)+b(,2)) is the carrying capacity, and C = K/N(,0) - 1, N(,0) being the initial population size (fixed). The covariance function was found to be dependent not only on time, order of the covariance, N(,0), r, and K, but also on a(,1), a(,2), b(,1) and b(,2);An approximating function for the covariance was developed using search techniques on the estimated covariance from the simulations. The variance and the covariance of the first order were computed theoretically from the transition probabilities for one case, and they were found to agree with the corresponding values of the approximating function;The approximating function found for the covariance function was used in an attempt to apply a quasi-maximum likelihood criterion in the estimation of the parameters of the logistic process. This and other methods of fitting the logistic curve to population size data were discussed, and they were compared in a Monte Carlo study. Linearization methods of fitting were found to be biased and some of them presented serious problems of estimation;Finally, the problem of goodness of fit was addressed, and the distribution of a (chi)(\u272) type statistic for goodness of fit was studied

There is life beyond the statistical significance

This article challenges the “tyranny of P-value” and promote more valuable and applicable interpretations of the results of research on health care delivery. We provide here solid arguments to retire statistical significance as the unique way to interpret results, after presenting the current state of the debate inside the scientific community. Instead, we promote reporting the much more informative confidence intervals and eventually adding exact P-values. We also provide some clues to integrate statistical and clinical significance by referring to minimal important differences and integrating the effect size of an intervention and the certainty of evidence ideally using the GRADE approach. We have argued against interpreting or reporting results as statistically significant or statistically non-significant. We recommend showing important clinical benefits with their confidence intervals in cases of point estimates compatible with results benefits and even important harms. It seems fair to report the point estimate and the more likely values along with a very clear statement of the implications of extremes of the intervals. We recommend drawing conclusions, considering the multiple factors besides P-values such as certainty of the evidence for each outcome, net benefit, economic considerations and values and preferences. We use several examples and figures to illustrate different scenarios and further suggest a wording to standardize the reporting. Several statistical measures have a role in the scientific communication of studies, but it is time to understand that there is life beyond the statistical significance. There is a great opportunity for improvement towards a more complete interpretation and to a more standardized reporting.Fil: Ciapponi, Agustín. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Centro de Investigaciones en Epidemiología y Salud Pública. Instituto de Efectividad Clínica y Sanitaria. Centro de Investigaciones en Epidemiología y Salud Pública; ArgentinaFil: Belizan, Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Centro de Investigaciones en Epidemiología y Salud Pública. Instituto de Efectividad Clínica y Sanitaria. Centro de Investigaciones en Epidemiología y Salud Pública; ArgentinaFil: Piaggio, Gilda. Instituto de Efectividad Clínica y Sanitaria; ArgentinaFil: Yaya, Sanni. Imperial College London; Reino Unido. University of Ottawa; Canad

The World Health Organization Fetal Growth Charts: A Multinational Longitudinal Study of Ultrasound Biometric Measurements and Estimated Fetal Weight.

BACKGROUND: Perinatal mortality and morbidity continue to be major global health challenges strongly associated with prematurity and reduced fetal growth, an issue of further interest given the mounting evidence that fetal growth in general is linked to degrees of risk of common noncommunicable diseases in adulthood. Against this background, WHO made it a high priority to provide the present fetal growth charts for estimated fetal weight (EFW) and common ultrasound biometric measurements intended for worldwide use. METHODS AND FINDINGS: We conducted a multinational prospective observational longitudinal study of fetal growth in low-risk singleton pregnancies of women of high or middle socioeconomic status and without known environmental constraints on fetal growth. Centers in ten countries (Argentina, Brazil, Democratic Republic of the Congo, Denmark, Egypt, France, Germany, India, Norway, and Thailand) recruited participants who had reliable information on last menstrual period and gestational age confirmed by crown-rump length measured at 8-13 wk of gestation. Participants had anthropometric and nutritional assessments and seven scheduled ultrasound examinations during pregnancy. Fifty-two participants withdrew consent, and 1,387 participated in the study. At study entry, median maternal age was 28 y (interquartile range [IQR] 25-31), median height was 162 cm (IQR 157-168), median weight was 61 kg (IQR 55-68), 58% of the women were nulliparous, and median daily caloric intake was 1,840 cal (IQR 1,487-2,222). The median pregnancy duration was 39 wk (IQR 38-40) although there were significant differences between countries, the largest difference being 12 d (95% CI 8-16). The median birthweight was 3,300 g (IQR 2,980-3,615). There were differences in birthweight between countries, e.g., India had significantly smaller neonates than the other countries, even after adjusting for gestational age. Thirty-one women had a miscarriage, and three fetuses had intrauterine death. The 8,203 sets of ultrasound measurements were scrutinized for outliers and leverage points, and those measurements taken at 14 to 40 wk were selected for analysis. A total of 7,924 sets of ultrasound measurements were analyzed by quantile regression to establish longitudinal reference intervals for fetal head circumference, biparietal diameter, humerus length, abdominal circumference, femur length and its ratio with head circumference and with biparietal diameter, and EFW. There was asymmetric distribution of growth of EFW: a slightly wider distribution among the lower percentiles during early weeks shifted to a notably expanded distribution of the higher percentiles in late pregnancy. Male fetuses were larger than female fetuses as measured by EFW, but the disparity was smaller in the lower quantiles of the distribution (3.5%) and larger in the upper quantiles (4.5%). Maternal age and maternal height were associated with a positive effect on EFW, particularly in the lower tail of the distribution, of the order of 2% to 3% for each additional 10 y of age of the mother and 1% to 2% for each additional 10 cm of height. Maternal weight was associated with a small positive effect on EFW, especially in the higher tail of the distribution, of the order of 1.0% to 1.5% for each additional 10 kg of bodyweight of the mother. Parous women had heavier fetuses than nulliparous women, with the disparity being greater in the lower quantiles of the distribution, of the order of 1% to 1.5%, and diminishing in the upper quantiles. There were also significant differences in growth of EFW between countries. In spite of the multinational nature of the study, sample size is a limiting factor for generalization of the charts. CONCLUSIONS: This study provides WHO fetal growth charts for EFW and common ultrasound biometric measurements, and shows variation between different parts of the world

Consort 2010 statement : extension to cluster randomised trials

Peer reviewedPublisher PD

Effect of dexamethasone on newborn survival at different administration-to-birth intervals: A secondary analysis of the who action (Antenatal corticosteroids for improving outcomes in preterm newborn)-I trial

Background: The WHO ACTION-I trial demonstrated that dexamethasone significantly reduced neonatal mortality when administered to women at risk of early preterm birth in low-resource countries. We conducted a secondary analysis to determine how these benefits can be optimised, by evaluating the effect of dexamethasone compared to placebo on newborn mortality and severe respiratory distress outcomes at different administration-to-birth intervals, and identifying the interval with the greatest benefits.Methods: The WHO ACTION-I trial was a multi-country, individually-randomised, parallel-group, double-blind, placebo-controlled trial. It was conducted in 29 hospitals across Bangladesh, India, Kenya, Nigeria, and Pakistan. Women with a viable singleton or multiple pregnancy who presented to participating hospitals at a gestational age of 26 weeks 0 days-33 weeks 6 days and who were at risk of imminent preterm birth were eligible. In this secondary analysis, 2638 women and their newborns treated with single course of dexamethasone or placebo were analysed. Multivariate logistic regression was used to assess the effect of dexamethasone versus placebo on neonatal death, stillbirth or neonatal death, and severe respiratory distress at 24 h and at 168 h, by administration-to-birth interval (from 0 through 28 days), adjusting for gestational age at first dose. We used relative risks to identify the administration-to-birth interval with the greatest benefits of dexamethasone compared to placebo on the newborn outcomes.Findings: Between 24 December 2017 and 21 November 2019, 2852 women and their 3070 babies were enrolled in the WHO ACTION-I trial; 1332 women (1464 babies) in the dexamethasone group and 1306 women (1440 babies) in the placebo group were included in this secondary analysis. Neonatal mortality risk was lower with increasing time between initiating dexamethasone and birth, achieving peak mortality reduction by days 13 and 14 and then diminishing as the interval approached 28 days, regardless of gestational age at administration. For other outcomes, the overall pattern of risk reduction extending into the second week was consistent with that of neonatal death.Interpretation: In women at risk of preterm birth prior to 34 weeks\u27 gestation, the neonatal benefits of antenatal dexamethasone appear to increase with longer administration-to-birth intervals than previously thought. This knowledge can support clinical assessment and estimation of the risks of adverse preterm newborn outcomes at the time of birth, and the potential benefits of antenatal dexamethasone treatment for a known administration-to-birth interval.Funding: Bill and Melinda Gates Foundation; World Health Organization

Duration of third stage labour and postpartum blood loss: a secondary analysis of the WHO CHAMPION trial data

Background: Obstetric haemorrhage continues to be a leading cause of maternal mortality, contributing to more than a quarter of the 2,443,000 maternal deaths reported between 2003 and 2009. During this period, about 70% of the haemorrhagic deaths occurred postpartum. In addition to other identifiable risk factors for greater postpartum blood loss, the duration of the third stage of labour (TSL) seems to be important, as literature shows that a longer TSL can be associated with more blood loss. To better describe the association between the duration of TSL and postpartum blood loss in women receiving active management of third stage of labour (AMTSL), this secondary analysis of the WHO CHAMPION trial data has been conducted. Methods: This was a secondary analysis of the WHO CHAMPION trial conducted in twenty-three sites in ten countries. We studied the association between the TSL duration and blood loss in the sub cohort of women from the CHAMPION trial (all of whom received AMTSL), with TSL upto 60 min and no interventions for postpartum haemorrhage. We used a general linear model to fit blood loss as a function of TSL duration on the log scale, arm and center, using a normal distribution and the log link function. We showed this association separately for oxytocin and for Heat stable (HS) carbetocin. Results: For the 10,040 women analysed, blood loss rose steeply with third stage duration in the first 10 min, but more slowly after 10 min. This trend was observed for both Oxytocin and HS carbetocin and the difference in the trends for both drugs was not statistically significant (p-value = 0.2070). Conclusions: There was a positive association between postpartum blood loss and TSL duration with either uterotonic. Blood loss rose steeply with TSL duration until 10 min, and more slowly after 10 min.Fil: Chikkamath, Sumangala B.. S. Nijalingappa Medical College; IndiaFil: Katageri, Geetanjali M.. S. Nijalingappa Medical College; IndiaFil: Mallapur, Ashalata A.. S. Nijalingappa Medical College; IndiaFil: Vernekar, Sunil S.. Jawaharlal Nehru Medical College Belgaum; IndiaFil: Somannavar, Manjunath S.. Jawaharlal Nehru Medical College Belgaum; IndiaFil: Piaggio, Gilda. No especifíca;Fil: Carroli, Guillermo. Centro Rosarino de Estudios Perinatales; ArgentinaFil: de Carvalho, José Ferreira. No especifíca;Fil: Althabe, Fernando. Organizacion Mundial de la Salud; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Centro de Investigaciones en Epidemiología y Salud Pública. Instituto de Efectividad Clínica y Sanitaria. Centro de Investigaciones en Epidemiología y Salud Pública; ArgentinaFil: Hofmeyr, G. Justus. University of Botswana; Estados Unidos. University of the Witwatersrand; SudáfricaFil: Widmer, Mariana. Organizacion Mundial de la Salud; ArgentinaFil: Gulmezoglu, Ahmet Metin. No especifíca;Fil: Goudar, Shivaprasad S.. Jawaharlal Nehru Medical College Belgaum; Indi

Comparison of two doses and two routes of administration of misoprostol after pre-treatment with mifepristone for early pregnancy termination

<p>Abstract</p> <p>Background</p> <p>It is not known whether a 400 μg dose of misoprostol has a similar efficacy as an 800 μg dose when administered sublingually or vaginally 24 hours after 200 mg mifepristone.</p> <p>Methods</p> <p>It is proposed to undertake a placebo-controlled, randomized, non-inferiority trial (3% margin of equivalence) of the two misoprostol doses when administered sublingually or vaginally using factorial design. A total of 3008 pregnant women (< 63 days of gestational age) who request legal termination of pregnancy will be recruited for the trial at 16 clinics in ten countries providing abortion services. Eligible women willing to join the study will be allocated randomly to one of the four treatment groups within each centre. Women in all treatment groups will first receive 200 mg mifepristone, followed 24 hours later by either 400 μg or 800 μg misoprostol, administered either sublingually or vaginally. The dose and route of administration of misoprostol will be blinded to women, each woman receiving four tablets vaginally and four tablets sublingually, two or four of which are 200 μg tablets of misoprostol and the rest are placebo tablets.</p> <p>The four treatment regimens will be compared in terms of: (i) their efficacy to induce complete abortion; (ii) induction-to-abortion interval when possible; (iii) the frequency of side effects; and (iv) women's perceptions. The initial judgment of the outcome of treatment is made at the follow-up visit on day 15 of the study and the final assessment four weeks later. It is estimated that the clinical phase will require 12–14 months for data collection.</p> <p>To compare the two routes and two doses, relative risks (RR) of failure to achieve a complete abortion and failure to terminate pregnancy and the two-sided 95% CIs will be calculated by standard methods, as well as risk differences and two-sided 95% CIs. The latter will be used to test the non-inferiority hypotheses (at 2.5% level of significance) for achieving complete abortion. The factorial structure will be taken into account in the analysis after testing the interaction.</p> <p>Trial registration</p> <p>ISRCTN87811512</p

Cluster randomized trial of an active, multifaceted information dissemination intervention based on The WHO Reproductive health library to change obstetric practices: methods and design issues [ISRCTN14055385]

BACKGROUND: Effective strategies for implementing best practices in low and middle income countries are needed. RHL is an annually updated electronic publication containing Cochrane systematic reviews, commentaries and practical recommendations on how to implement evidence-based practices. We are conducting a trial to evaluate the improvement in obstetric practices using an active dissemination strategy to promote uptake of recommendations in The WHO Reproductive Health Library (RHL). METHODS: A cluster randomized trial to improve obstetric practices in 40 hospitals in Mexico and Thailand is conducted. The trial uses a stratified random allocation based on country, size and type of hospitals. The core intervention consists of three interactive workshops delivered over a period of six months. The main outcome measures are changes in clinical practices that are recommended in RHL measured approximately a year after the first workshop. RESULTS: The design and implementation of a complex intervention using a cluster randomized trial design are presented. CONCLUSION: Designing the intervention, choosing outcome variables and implementing the protocol in two diverse settings has been a time-consuming and challenging process. We hope that sharing this experience will help others planning similar projects and improve our ability to implement change

WHO systematic review of maternal mortality and morbidity: methodological issues and challenges

BACKGROUND: Reducing maternal mortality and morbidity are among the key international development goals. A prerequisite for monitoring the progress towards attainment of these goals is accurate assessment of the levels of mortality and morbidity. In order to contribute to mapping the global burden of reproductive ill-health, we are conducting a systematic review of incidence and prevalence of maternal mortality and morbidity. METHODS: We followed the standard methodology for systematic reviews. We prepared a protocol and a form for data extraction that identify key characteristics on study and reporting quality. An extensive search was conducted for the years 1997–2002 including electronic and hand searching. RESULTS: We screened the titles and abstracts of about 65,000 citations identified through 11 electronic databases as well as various other sources. Four thousand six hundred and twenty-six full-text reports were critically appraised and 2443 are included in the review so far. Approximately one third of the studies were conducted in Asia and Africa. The reporting quality was generally low with definitions for conditions and the diagnostic methods often not reported. CONCLUSIONS: There are unique challenges and issues regarding the search, critical appraisal and summarizing epidemiological data in this systematic review of prevalence/incidence studies. More methodological studies and discussion to advance the field will be useful. Considerable efforts including leadership, consensus building and resources are required to improve the standards of monitoring burden of disease