Extreme(ly) mean(ingful): Sequential formation of a quality group

The present paper studies the limiting behavior of the average score of a sequentially selected group of items or individuals, the underlying distribution of which, $F$, belongs to the Gumbel domain of attraction of extreme value distributions. This class contains the Normal, Lognormal, Gamma, Weibull and many other distributions. The selection rules are the "better than average" ($\beta=1$) and the "$\beta$-better than average" rule, defined as follows. After the first item is selected, another item is admitted into the group if and only if its score is greater than $\beta$ times the average score of those already selected. Denote by $\bar{Y}_k$ the average of the $k$ first selected items, and by $T_k$ the time it takes to amass them. Some of the key results obtained are: under mild conditions, for the better than average rule, $\bar{Y}_k$ less a suitable chosen function of $\log k$ converges almost surely to a finite random variable. When $1-F(x)=e^{-[x^{\alpha}+h(x)]}$, $\alpha>0$ and $h(x)/x^{\alpha}\stackrel{x\rightarrow \infty}{\longrightarrow}0$, then $T_k$ is of approximate order $k^2$. When $\beta>1$, the asymptotic results for $\bar{Y}_k$ are of a completely different order of magnitude. Interestingly, for a class of distributions, $T_k$, suitably normalized, asymptotically approaches 1, almost surely for relatively small $\beta\ge1$, in probability for moderate sized $\beta$ and in distribution when $\beta$ is large.Comment: Published in at http://dx.doi.org/10.1214/10-AAP684 the Annals of Applied Probability (http://www.imstat.org/aap/) by the Institute of Mathematical Statistics (http://www.imstat.org

ECONOMIC ANALYSIS OF COWPEA PRODUCTION IN NIGERIA

This study employs a stochastic frontier production function analysis to examine the productivity and technical efficiency of cowpea production in Adamawa State, Nigeria and also to identify the factors affecting the technical inefficiency using farm level survey data collected from 150 cowpea farmers selected using multi stage sampling technique. Findings from the analysis show that cowpea farmers operated on a very small scale and are profitable. The productivity analysis shows that agro chemicals, fertilizer, farm size and labor were all positively and significantly related to the technical efficiency. The return to scale (RTS) of 0.9904 shows that cowpea production was in the rational stage of the production surface. The technical efficiency varies from 0.1094 to 0.9568 with a mean technical efficiency of 0.6649, indicating that farmers were operating below the efficiency frontier. Thus, in the short run, there is a scope to increase output by 34%. The inefficiency model revealed that education of the farmers; extension visits and access to credit are the main factors that affect technical efficiency of the farmers

Assessment of average radiation dose for abdominal computed tomography examinations in Aminu Kano Teaching Hospital, Kano

The demand for abdominal Computed Tomography (CT) scans has dramatically increased over the years due to its higher sensitivity in ruling out a wide range medical conditions as compared to other imaging modalities. However, this patronage is associated with high effective dose and hence attributable to the risk of radiation-induced injuries. Establishing an acceptable radiation dose level and designing a protocol of maintaining dose level within that range is a sure optimization practice that is recommended by most national and international radiation monitoring bodies. The study aims to assess the average radiation dose received by patients undergoing abdominal CT examinations in Radiology unit of AKTH Kano, Nigeria. Dose survey of 100 adult abdominal CT scans in Radiology department of AKTH from June-October 2018. CTDIvol and DLP were simply obtained from the CT machine as displayed on the console and recorded into an adapted IAEA survey form. Effective dose was estimated by multiplying DLP by the conversion factor, k-value for abdomen (0.015mSv/mGy.cm). A total of 100 patient’s radiation dose summary comprising 57 (57%) of females and 43 (43%) males with a mean age of 46 years. Determined 75th percentile CTDIvol, DLP and effective doses for abdominal CT were found to be 12 mGy, 2225.25 mGy.cm and 33.38 mSv respectively. The CTDIvol value was lower than most local and international established studies. The DLP and effective doses of the present study were significantly higher than other studies and calls for review of existing protocol to optimize practice.Keywords: Abdominal CT, DRL, Effective dos

Sonographic Dimension of Fetal Nuchal Translucency in Kano Metropolis: A single Center Study

Background: Nuchal Translucency Thickness (NTT) is a hypo-echoic region of subcutaneous fluid accumulation in the posterior neck region at the  level of the cervical spine between the skin and soft tissues and is mostly found at 11–13 weeks of fetal gestation. It is visualised with a mid-sagittal  ultrasound view of the fetus in a neutral position. The NTT provides a risk assessment for chromosomal abnormalities which has been used as a  marker of possible fetal abnormalities. Hence, the justification to conduct the present study. Aim: To establish the mean fetal nuchal translucency thickness with corresponding gestational age (GA) and to assess the correlation between  Crown Rump Length (CRL), GA, and NTT among apparently healthy pregnant women. Methods: A cross-sectional study was conducted among 150 apparently normal consenting pregnant women in their late first trimester in the  Radiology department of Muhammad Abdullahi Wase Teaching Hospital, Kano from February 2021 to May 2021. Ultrasonographic measurements of  the crown-rump length (CRL), gestational age (GA), and NTT were performed on pregnancies within 11 to 13 weeks of gestation. Their 2.5th,  25th, median and 97.5th percentiles of the NTT, GA, and CRL were determined using SPSS version 23 (IBM, 2017). Indicate correlation… as part of  the analysis. Results: Median NTT at 11-13+6 weeks of gestation was found as 3.0±0.10mm. The NT thickness increased with increasing CRL and gestational  week in the first trimester. The correlation coefficient between NTT and CRL as well as GA were 0.472 and 0.451, respectively. Conclusion: The  overall mean NTT in Kano fetuses was determined. These should be useful for first-trimester screening in ruling out potential fetal chromosomal  abnormalities in Kano, Nigeria

The Noisy Secretary Problem and Some Results on Extreme Concomitant Variables

The classical secretary problem for selecting the best item is studied when the actual values of the items are observed with noise. One of the main appeals of the secretary problem is that the optimal strategy is able to find the best observation with the nontrivial probability of about 0.37, even when the number of observations is arbitrarily large. The results are strikingly di↵erent when the quality of the secretaries are observed with noise. If there is no noise, then the only information that is needed is whether an observation is the best among those already observed. Since observations are assumed to be i.i.d. this is distribution free. In the case of noisy data, the results are no longer distrubtion free. Furthermore, one needs to know the rank of the noisy observation among those already seen. Finally, the probability of finding the best secretary often goes to 0 as the number of obsevations, n, goes to infinity. The results depend heavily on the behavior of pn, the probability that the observation that is best among the noisy observations is also best among the noiseless observations. Results involving optimal strategies if all that is available is noisy data are described and examples are given to elucidate the results

Seroprevalence of Hepatitis C Virus (HCV) antibodies in pregnant women in Anyigba, Kogi State, North Central Nigeria

Background: Hepatitis C virus (HCV) infection is a major public health concern. The aim of this study was  to ascertain the seroprevalence and risk factors of HCV antibodies among pregnant women in  Anyigba, Kogi State North Central Nigeria.Materials and methods:Blood samples (5mls) were collected from one hundred and thirty consenting pregnant women attending antenatal clinic in Grimad hospital and eighty non-pregnant women from the out-patient clinic were screened for the presence of HCV antibodies. This was done by Skytech diagnostic  laboratory rapid strip (USA) and confirmed by ELISA method.Results: Out of 130 pregnant women 9(6.9%) were confirmed to be positive to HCV antibodies. Also out of 80 non-pregnant women of the same age group, used as control, 4(5.0%) were positive.Conclusion: A prevalence rate of 6.9% calls for urgent attention by policy makers and healthcare providers to begin massive enlightenment of this problem. All pregnant women should be screened for early detection.Keywords: Hepatitis C Virus, Pregnancy, Screening, Transmission

¿Cómo casi destruir un mercado sin querer y no fallar en el intento? El caso del impuesto sobre los automóviles de lujo en Argentina

Under the pressure of a growing capital outflow, by the end of 2013 the Argentine government implemented what was known as the tax on "luxury cars". Even when not explicitly declared, the main objective was to reduce imports of most expensive cars to reduce the trade deficit of the automotive sector, which was contributing heavily to the capital account deficit. Even when the policy could be categorized as "successful" in terms of reducing a USD 4.5 billion deficit in 2013 to one of just over USD 0.7 billion in 2014, it had a devastating and lasting impact on the internal market, that just in 2013 had achieved a record in sales. We obtain that during the first year of the implementation of the tax, the overall impact on sales of models reached by the tax was 53.7%. Despite some differences, the negative impact took place throughout the whole year. Not surprisingly, cars reached by the highest tax rate were most affected, as well as carmakers that produce more expensive varieties. However, even when the measure may have been designed to have a direct impact on a small part of the market, the negative effects extended to the whole market.Bajo la presión de una creciente salida de capitales, a fines del año 2013 el gobierno argentino implementó lo que se conoció como el impuesto a los "autos de lujo". Aunque no declarado explícitamente, el objetivo principal era reducir las importaciones de los automóviles más caros para reducir el déficit comercial del sector automotriz, que contribuía de manera importante al déficit de la cuenta de capital. Más allá del hecho de que la política podría calificarse de "exitosa" en cuanto a la reducción de un déficit de USD 4.500 millones en 2013 a uno de poco más de USD 700 millones en 2014, tuvo un impacto devastador y duradero en el mercado interno, que apenas un año antes, en 2013, había alcanzado un récord de ventas. Los resultados muestran que durante el primer año de la aplicación del impuesto, el impacto global en las ventas de los modelos alcanzados por el mismo fue del 53,7%. A pesar de algunas diferencias, el impacto negativo se produjo a lo largo todo el año 2014. No sorprende que los automóviles alcanzados por la tasa del 50% fueran los más afectados, así como los fabricantes de modelos más caros. Sin embargo, incluso cuando la medida puede haber sido diseñada para tener un impacto directo en una pequeña parte del mercado, los efectos negativos se extendieron a la totalidad del mismo.