Moo-cow! Mummy! More! How do children learn so many words?

Learning the words of your language is a huge challenge for children. In particular, it is a challenge of scale. At least 40,000 words have to be learnt. At 18 months a child's vocabulary starts to explode. How do they do it? Bob McMurray says it is all to down to statistics.     

Do you sincerely want to be cited? Or: read before you cite

Do you sincerely want to be cited? Prestige depends on the number of times your academic paper gets cited. But that need not be a measure of how good it is, nor even of how many times it is actually read. Mikhail Simkin and Vwani Roychowdhury explain their theory of the unread citation.     

Drug contamination of banknotes

When the police or Customs and Excise seize currency they are nowadays likely to have the confiscated banknotes tested for the presence of cocaine, heroin, ecstasy and cannabis. It is an interesting statistic that there is a 99% chance that "the money in your pocket" will be contaminated with detectable amounts of cocaine. Contamination by the other drugs is apparently not so prevalent, but it is clear that banknotes in general circulation are not completely free from such contamination, albeit at a lower level. Just how low, Patrick Laycock explains, has become a source of dispute.     

The Access/Impact Problem and the Green and Gold Roads to Open Access: An Update

The research access/impact problem arises because journal articles are not accessible to all of their would-be users; hence, they are losing potential research impact. The solution is to make all articles open access (OA, i.e., accessible online, free for all). OA articles have significantly higher citation impact than non-OA articles. There are two roads to OA: the “golden” road (publish your article in an OA journal) and the “green” road (publish your article in a non-OA journal but also self-archive it in an OA archive). About 10% of journals are gold, but over 90% are already green (i.e., they have given their authors the green light to self-archive); yet only about 10–20% of articles have been self-archived. To reach 100% OA, self-archiving needs to be mandated by researchers’ employers and funders, as they are now increasingly beginning to do.     

A Note on the Inverse Birthday Problem With Applications

The classical birthday problem considers the probability that at least two people in a group of size N share the same birthday. The inverse birthday problem considers the estimation of the size N of a group given the number of different birthdays in the group. In practice, this problem is analogous to estimating the size of a population from occurrence data only. The inverse problem can be solved via two simple approaches including the method of moments for a multinominal model and the maximum likelihood estimate of a Poisson model, which we present in this study. We investigate properties of both methods and show that they can yield asymptotically equivalent Wald-type interval estimators. Moreover, we show that these methods estimate a lower bound for the population size when birth rates are nonhomogenous or individuals in the population are aggregated. A simulation study was conducted to evaluate the performance of the point estimates arising from the two approaches and to compare the performance of seven interval estimators, including likelihood ratio and log-transformation methods. We illustrate the utility of these methods by estimating: (1) the abundance of tree species over a 50-hectare forest plot, (2) the number of Chlamydia infections when only the number of different birthdays of the patients is known, and (3) the number of rainy days when the number of rainy weeks is known. Supplementary materials for this article are available online.     

A Note on the Uniformity Assumption in the Birthday Problem

If 23 people are selected at random from some large population whose birthdays are uniformly distributed throughout the year, then it is well-known that the chances are better than even that at least two of them will have the same birthday. In this note it is shown that this is true for any distribution of birthdays.     

The Access/Impact Problem and the Green and Gold Roads to Open Access

The research access/impact problem arises because journal articles are not accessible to all of their would-be users; hence, they are losing potential research impact. The solution is to make all articles Open Access (OA; i.e., accessible online, free for all). OA articles have significantly higher citation impact than non-OA articles. There are two roads to OA: the “golden” road (publish your article in an OA journal) and the “green” road (publish your article in a non-OA journal but also self-archive it in an OA archive). Only 5% of journals are gold, but over 90% are already green (i.e., they have given their authors the green light to self-archive); yet only about 10–20% of articles have been self-archived. To reach 100% OA, self-archiving needs to be mandated by researchers' employers and funders, as the United Kingdom and the United States have recently recommended, and universities need to implement that mandate.     

The Access/Impact Problem and the Green and Gold Roads to Open Access

Abstract

The research access/impact problem arises because journal articles are not accessible to all of their would-be users; hence, they are losing potential research impact. The solution is to make all articles Open Access (OA; i.e., accessible online, free for all). OA articles have significantly higher citation impact than non-OA articles. There are two roads to OA: the “golden” road (publish your article in an OA journal) and the “green” road (publish your article in a non-OA journal but also self-archive it in an OA archive). Only 5% of journals are gold, but over 90% are already green (i.e., they have given their authors the green light to self-archive); yet only about 10–20% of articles have been self-archived. To reach 100% OA, self-archiving needs to be mandated by researchers' employers and funders, as the United Kingdom and the United States have recently recommended, and universities need to implement that mandate.     

The truth about those little red lights: a tale of power and poppycock

Leaving your electrical appliances on standby wastes-how much? Up to 10% of the electricity supply. Everyone knows that. Or is it 8%? Or 3%? Anyway, it is a lot, and the statistic has acquired a life of its own. Matthew Parris's article from The Times of July 22nd, 2006, was runner-up in the 2007 Royal Statistical Society competition for journalists writing on a statistical theme. The Chancellor he refers to, one Gordon Brown, is now, of course, the Prime Minister.     

Scatterplots

A pair of axes, a few data points liberally distributed around, click on the mouse and your software will sort you out a scatterplot. Or will it? R. Allan Reese can tell you better.     

MATRIX ANALYSIS OF THE CASH FLOWS AND RESERVES OF A LIFE OFFICE

Matrix projection methods have been used by demographers to prove a number of powerful general theorems concerning population growth and development. The methods have also been applied to the study of graded social systems and to problems of manpower planning. The policy-holders of a life office and the members of a superannuation fund belong to graded systems with age as the important hierarchical variable. The abovementioned methods can therefore be used to study the growth and development of the membership of these institutions.
Recent articles by Sherris (1977), and Pollard and Sherris (1979a, 1979b) have shown that matrix analysis is also very useful for projecting the cash flows and reserves of life assurance companies and superannuation funds.
In this paper the use of these methods is illustrated by the projection of the reserves of a life office writing whole-life assurance contracts. We find that as the fund matures, it grows exponentially.     

电影首映日后票房预测模型研究

利用285部电影的截面数据进行单样本t检验,发现票房过亿电影的首映日票房都不少于200万元。抽取138部首映日票房超过200万元的电影的21天数据构建动态面板模型,采用两步系统GMM估计建立票房预测模型。研究表明:前一日票房对后一日票房具有显著正向影响,即在一段时间内前一日票房增加将提升后一日票房。票价较高和较低都会对票房产生积极影响,因此将票价纳入票房预测模型中。电影类型、上映日期、上映档期、出品国别、续集、网络评分、点映活动均被证明对票房具有正向影响。相较其他研究,包含上述指标的预测模型准确率得到了大幅提高。     

Two Birthday Problems

ABSTRACT

This article focuses on two birthday problems which naturally follow from the most common birthday problems taught in statistics courses. The solutions to these new problems provide a good illustration of several combinatorial techniques.     

Poisson approximation and dna sequence matching

The Poisson distribution is commonly used to model the number of occurrences of independent rare events. However, many instances arise where dependence exists, for example, in counting the length of long head runs in coin tossing, or matches between two DNA sequences. The Chen-Stein method of Poisson approximation yields bounds on the error incurred when approximating the number of occurrences of possibly dependent events by a Poisson random variable of the same mean. In addition to the problems related to the motivating examples from molecular biology involving runs and matches, the method may be applied to questions as varied as calculating probabilities involving extremes of sequences of random variables and approximating the probability of general birthday coincidences.     

Anna Karenina and the two envelopes problem

The Anna Karenina principle is named after the opening sentence in the eponymous novel: Happy families are all alike; every unhappy family is unhappy in its own way. The two envelopes problem (TEP) is a much-studied paradox in probability theory, mathematical economics, logic and philosophy. Time and again a new analysis is published in which an author claims finally to explain what actually goes wrong in this paradox. Each author (the present author included) emphasises what is new in their approach and concludes that earlier approaches did not get to the root of the matter. We observe that though a logical argument is only correct if every step is correct, an apparently logical argument which goes astray can be thought of as going astray at different places. This leads to a comparison between the literature on TEP and a successful movie franchise: it generates a succession of sequels, and even prequels, each with a different director who approaches the same basic premise in a personal way. We survey resolutions in the literature with a view to synthesis, correct common errors, and give a new theorem on order properties of an exchangeable pair of random variables, at the heart of most TEP variants and interpretations. A theorem on asymptotic independence between the amount in your envelope and the question whether it is smaller or larger shows that the pathological situation of improper priors or infinite expectation values has consequences as we merely approach such a situation.     

Streamlining Acquisition Workflows Through Collaboration and Innovation

Abstract

As a selector, have you ever wondered if the resource you requested was ordered? As an acquisitions staff member, are you struggling with keeping track of your order requests from various channels? As a manager, are you finding it challenging to monitor staff work? CORAL, an open source electronic resource management system, proved to be one solution to these concerns for North Carolina State University (NCSU) Libraries. This article discusses how to manage workflows in CORAL and outlines a NCSU initiative to evolve this tool through collaboration across departments and across the CORAL community.     

中国高技术产业R&D资本折旧率的测算

2008年SNA将R&D并入到资产核算的范畴,但是将这一想法付诸实践面临诸多问题,难题之一就是R&D资本折旧率的选取。选择C-D生产函数、一级CES生产函数、二级CES生产函数和超越对数生产函数估算了中国高技术产业R&D资本折旧率,结果显示,医药制造业、航空航天器及设备制造业、电子及通信设备制造业、计算机及办公设备制造业和医疗设备及仪器仪表制造业的R&D资本折旧率分别为20%、31.5%、25.25%、41.5%和31.3%。并且,在此基础上估算了五个行业的R&D资本存量,从平均增长率来看,计算机及办公设备制造业最快,其次是电子及通信设备制造业,医疗仪器设备及仪器仪表制造业和医药制造业相差不大,最慢的是航空、航天器及设备制造业。     

Credit this: how the banks decide your credit score

In February, internet bank Egg announced its decision to cancel the credit cards of 161 000 of its customers. Egg were "not comfortable with the level of risk" that these customers represented. Bank customers are judged by their credit scores. So what is credit scoring? How do lenders assess your creditworthiness? And how can you improve your credit score with them? David Edelman provides some answers.     

A modified least-failures sampling procedure for bernoulli subset selection

We restrict attention to a class of Bernoulli subset selection procedures which take observations one-at-a-time and can be compared directly to the Gupta-Sobel single-stage procedure. For the criterion of minimizing the expected total number of observations required to terminate experimentation, we show that optimal sampling rules within this class are not of practical interest. We thus turn to procedures which, although not optimal, exhibit desirable behavior with regard to this criterion. A procedure which employs a modification of the so-called least-failures sampling rule is proposed, and is shown to possess many desirable properties among a restricted class of Bernoulli subset selection procedures. Within this class, it is optimal for minimizing the number of observations taken from populations excluded from consideration following a subset selection experiment, and asymptotically optimal for minimizing the expected total number of observations required. In addition, it can result in substantial savings in the expected total num¬ber of observations required as compared to a single-stage procedure, thus it may be de¬sirable to a practitioner if sampling is costly or the sample size is limited.     

Methods for Studying Generalized Birthday and Coupon Collection Problems

In this paper, we consider generalizations of two classical probability problems: the birthday problem and the coupon collector's problem. These problems are discussed in terms of urn models and captured through generating functions. Some methods for the study of the problems are presented. Furthermore, we also formulate the generalized birthday and coupon collector's problems as the waiting time problems. In each case, numerical examples are given in order to illustrate the feasibility of our methods.