Relevant Statistic Research Articles

Mortality from time of listing for transplantation as an indicator of candidate outcomes

Survival after transplantation has traditionally been the statistic most closely scrutinized as to the efficacy of the procedure and a program's performance. We propose that mortality from the time of listing is a more significant outcome measure for potential transplant candidates. We present our lung transplant program's outcomes using this measure. An analysis was performed on all patients listed for lung transplantation at our institution between 1997 and 2002. Kaplan-Meier analyses of survival at 1, 2, and 3 years after listing were assessed. One hundred forty-eight patients qualified for the analysis; of these, 96 received transplants. The median time to transplantation was 142 days. Twenty-five of the patients died while waiting for a transplant. The median time to death for these patients was 311 days. Of the 27 transplant recipients who died, the median time from listing to death was 547 days. The 1-, 2-, and 3-year mortality rates after being listed were 20.0%, 32.4%, and 39.7%, respectively, for all patients. Mortality after listing is a more relevant statistic for prospective transplant candidates. Intraprogram comparisons of listed nontransplant survival to listed transplant survival may facilitate the acceptance of sicker patients for transplant consideration. It may also help foster the development of an "alternate" list for transplantation and prove useful in helping determine organ prioritization.

Mortality from time of listing for transplantation as an indicator of candidate outcomes.

Survival after transplantation has traditionally been the statistic most closely scrutinized as to the efficacy of the procedure and a program's performance. We propose that mortality from the time of listing is a more significant outcome measure for potential transplant candidates. We present our lung transplant program's outcomes using this measure. An analysis was performed on all patients listed for lung transplantation at our institution between 1997 and 2002. Kaplan-Meier analyses of survival at 1, 2, and 3 years after listing were assessed. One hundred forty-eight patients qualified for the analysis; of these, 96 received transplants. The median time to transplantation was 142 days. Twenty-five of the patients died while waiting for a transplant. The median time to death for these patients was 311 days. Of the 27 transplant recipients who died, the median time from listing to death was 547 days. The 1-, 2-, and 3-year mortality rates after being listed were 20.0%, 32.4%, and 39.7%, respectively, for all patients. Mortality after listing is a more relevant statistic for prospective transplant candidates. Intraprogram comparisons of listed nontransplant survival to listed transplant survival may facilitate the acceptance of sicker patients for transplant consideration. It may also help foster the development of an "alternate" list for transplantation and prove useful in helping determine organ prioritization.

Geometric Return and Portfolio Analysis

Expected geometric return is routinely reported as a summary measure of the prospective performance of asset classes and investment portfolios. It has intuitive appeal because its historical counterpart, the geometric average, provides a useful annualised measure of the proportional change in wealth that actually occurred over a past time series, as if there had been no volatility in return. However, as a prospective measure, expected geometric return has limited value and often the expected annual arithmetic return is a more relevant statistic for modelling and analysis. Despite this, the distinction between expected annual arithmetic return and expected geometric return is not well understood, both in respect of individual asset classes and in respect of portfolios. This confusion persists even though it is explained routinely in finance textbooks and other reference sources. Even the supposedly straightforward calculation of weighted average portfolio return becomes somewhat complicated, and can produce counterintuitive results, if the focus of future-orientated reporting is expected geometric return. This paper explains these issues and applies them in the context of the calculations underlying the projections for the New Zealand Superannuation Fund.

Intercambio de alumnos. Una experiencia de internacionalización de la educación

This paper takes up the experience developed by the Pontificia Universidad Católica de Chile (PUC) in international students’ exchange. It analyses the effect that this process has had regarding not only the pupils taking part in it, but also the teaching enrichment, due to the presence of foreign visitors. It explains, very briefly, the multiplying effect that has favoured other tasks, as a consequence of the interchange’s agreements, and, finally, it points out its evolution through the most relevant statistic data.

Analysis of the expansion of the built-up area of Dalian city

With the astounding development and gradual improvement of remote sensing technology, as an advanced science technology, it is used to provide multi-temporal, large scope real-time information for land-use dynamic change, and also is one of the best efficient methods for studying the earth resources and environment. Remote sensing image has its characteristics of ample information and reflecting the objective realities. The paper uses multi-temporal TM images in 1986, 1996 and 2000, and relevant statistic data to analyze land-use changes of Dalian City in Liaoning Province of China over ten years by means of the correlation analysis method. The results have shown that two methods could conformably reflect the present land-use change. Urbanization is closely correlative to natural factors and economic development. Especially in recent 20 years, under the influence of the reform and open-up policy, Dalian, as a specific coast city, is becoming an international metropolis.

Regression models of volume increment percentage in the Most represented stands of coniferous tree species in Serbia

Considering the great significance of volume increment in forestry, it is understandable that there are numerous methods of its assessment. However, all these methods have some disadvantages, either the accuracy of the obtained results, too large scope of works of forest inventory (economicity), or the restriction only to stands of certain silvicultural type. To make the method of stand volume increment more economic and simplified, we defined regression models for volume increment percentage assessment in fir, spruce, Austrian pine and Scots pine stands in Serbia. Empirical data were fitted by four regression models for each tree species. The criteria for the final selection of models for the determination of volume increment percentage were the relevant statistic parameters of regression and correlation analysis, and the degree of concordance of "real" and fitted ("table") values of volume increment percentage. The selected models for the above tree species are Fir Spruce Austrian pine Scots pine In the practical work of the assessment of current volume increment in the stand, in regular forest inventories, the method of volume increment percentage should be implemented with correction factors for the fitting of "table" (obtained by this method) values of volume increment and "real" values (obtained by the method of diameter increment), on at least 10 % of the stands of the same or similar stand class (same or similar tree species and stand form). In this way, the costs of forest inventory would be reduced, and the obtained results would range within the limits of the required accuracy .

Enhancing Students' Understanding of Risk and Geologic Hazards Using a Dartboard Model

Magnitude-frequency relationships of natural hazards can be expressed in a visual form through a dartboard model. The rings of the dartboard can be drawn to represent magnitude, exceedance probability, average recurrence interval, or any other relevant statistic. Dartboards can be constructed from magnitude-frequency functions or from historical data, making it possible to model a wide variety of hazards. The dartboards can be used to engage students at different levels of preparation, in different contexts, and for different lengths of time: “playing” the dart game may consist of conducting a thought experiment, actually throwing at a physical dartboard, or simulating events based on a computer program. Playing the dart game helps students to understand how a magnitude-frequency relationship results from a sequence of events. Dartboards mitigate the misconception that processes occur periodically (e.g., “the 100-year flood”) by emphasizing the random nature of hazards. The dart game also helps students to visualize the long-term consequences of living in a hazardous location. Dart games provide a context in which geoscience students can learn about statistics, simulations, and the testing of models against data.

A 4D approach to the analysis of functional brain images: Application to FMRI data

This paper presents a new approach to functional magnetic resonance imaging (FMRI) data analysis. The main difference lies in the view of what comprises an observation. Here we treat the data from one scanning session (comprising t volumes, say) as one observation. This is contrary to the conventional way of looking at the data where each session is treated as t different observations. Thus instead of viewing the v voxels comprising the 3D volume of the brain as the variables, we suggest the usage of the vt hypervoxels comprising the 4D volume of the brain-over-session as the variables. A linear model is fitted to the 4D volumes originating from different sessions. Parameter estimation and hypothesis testing in this model can be performed with standard techniques. The hypothesis testing generates 4D statistical images (SIs) to which any relevant test statistic can be applied. In this paper we describe two test statistics, one voxel based and one cluster based, that can be used to test a range of hypotheses. There are several benefits in treating the data from each session as one observation, two of which are: (i) the temporal characteristics of the signal can be investigated without an explicit model for the blood oxygenation level dependent (BOLD) contrast response function, and (ii) the observations (sessions) can be assumed to be independent and hence inference on the 4D SI can be made by nonparametric or Monte Carlo methods. The suggested 4D approach is applied to FMRI data and is shown to accurately detect the expected signal.

An Efficient Alternative to Average Ranks for Testing with Incomplete Ranking Data

In this paper we consider the setting where a group of n judges are to independently rank a series of k objects, but the intended complete rankings are not realized and we are faced with analyzing randomly incomplete ranking vectors. In this paper we propose a new testing procedure for dealing with such data realizations. We concentrate on the problem of testing for no differences in the objects being ranked (i.e., they are indistinguishable) against general alternatives, but our approach could easily be extended to restricted (e.g., ordered or umbrella) alternatives. Using an improvement of a preliminary screening approach previously proposed by the authors, we present an algorithm for computation of the relevant Friedman-type statistic in the general alternatives setting and present the results of an extensive simulation study comparing the new procedure with the standard approach of imputing average within-judge ranks to the unranked objects.

Bit error probability for MDPSK and NCFSK over arbitrary Rician fading channels

In this paper, we analyze the bit error probability (BEP) of binary and quaternary differential phase shift keying (2/4 DPSK) and noncoherent frequency shift keying (NCFSK) with postdetection diversity combining in arbitrary Rician fading channels. The model is quite general in that it accommodates fading correlation and noise correlation between different diversity branches as well as between adjacent symbol intervals. We show that the relevant decision statistic can be expressed in a noncentral Gaussian quadratic form, and its moment generating function (MGF) is derived. Using the MGF and the saddle point technique, we give an efficient numerical quadrature scheme to compute the BEP. The most significant contribution of the paper, however, lies in the derivation of a closed-form cumulative distribution function (cdf) for the decision statistic. As a result, a closed-form BEP expression in the form of an infinite series of elementary functions is developed, which is general and unifies previous published BEP results for 2/4 DPSK and NCFSK for multichannel reception in Rician fading. Specialization to some important cases are discussed and, as a byproduct, a new and general finite-series expression for the BEP in arbitrarily correlated Rayleigh fading is obtained. The theory is applied to study 2/4 DPSK and NCFSK performance for independent and correlated Rician fading channels; and some interesting findings are presented.

Antecedents of green purchases: a survey in China

Examines the influence of cultural values, ecological affect and ecological knowledge on the green purchasing behavior of Chinese consumers. Using structural equation modeling to assess the significance that ecological affect and ecological knowledge have on green purchase intention and actual green purchase, the results demonstrate that a strong positive relationship exists. However, other important findings suggest that Chinese people’s level of ecological knowledge is low and actual green purchase behavior minimal. Yet in contrast, Chinese consumers express a positive ecological affect and green purchase intention. In relation to the hypothesis that the Chinese strongly adhere to the cultural value of living in harmony with nature, the relevant descriptive statistic shows that today’s Chinese only pay moderate allegiance to this “man‐nature” orientation. Moreover, this cultural value is only found to exert significant bearing on ecological affect but not ecological knowledge.

A Martingale-based bootstrap inference with censored data

In this paper, me shall investigate a bootstrap method hasd on a martingale representation of the relevant statistic for inference to a class of functionals of the survival distribution. The method is similar in spirit to Efron's (1981) bootstrap, and thus in the present paper will be referred to as “martingale-based bootstrap” The method was derived from Lin,Wei and Ying (1993), who appiied the method in checking the Cox model with cumulative sums of martingale-based residuals. It is shown that this martingale-based bootstrap gives a correct first-order asymptotic approximation to the distribution function of the corresponding functional of the Kaplan-Meier estimator. As a consequence, confidence intervals constructed by the martingale-based bootstrap have asymptotially correct coverage probability. Our simulation study indicats that the martingale-based bootst strap method for a small and moderate sample sizes can be uniformly better than the usual bootstrap method in estimating the sampling distribution for a mean function and a point probability in survival analysis.

On the Underfitting and Overfitting Sets of Models Chosen by Order Selection Criteria

For a general class of order selection criteria, we establish analytic and non-asymptotic evaluations of both the underfitting and overfitting sets of selected models. These evaluations are further specified in various situations including regressions and autoregressions with finite or infinite variances. We also show how upper bounds for the misfitting probabilities and hence conditions ensuring the weak consistency can be derived from the given evaluations. Moreover, it is demonstrated how these evaluations, combined with a law of the iterated logarithm for some relevant statistic, can provide conditions ensuring the strong consistency of the model selection criterion used.

A Screening Analysis for Incomplete Ranking Data

We consider the setting where a group of n judges are to rank independently a series of k objects. When all judges rank all treatments, this coincides with the no-interaction two-way lay-out setting with one observation per cell. However, many times the intended complete rankings are not realized and we are faced with analysing randomly incomplete rank vectors. We propose a new screening approach to analysing such data realizations. For discussion, we concentrate on the problem of testing for no differences in the objects being ranked (i.e. they are indistinguishable) against general alternatives, but our approach will also be quite appropriate for restricted (e.g. ordered or umbrella) alternatives. We detail the algorithm for computation of the relevant Friedman-type statistic in the general alternatives setting and present the results of a simulation study to assess the effectiveness of the algorithm.

Bacterial contamination of breast milk collected through manual expression and stored at room temperature

OBJECTIVES: To the determine the bacterial contamination profile of unheated expressed breast milk, collected without rigid hygienic precautions and stored at room temperature for nine hours. The purpose was to give poor lactating mothers the alternative of storing their own milk out of refrigerator. A research on cultural, social and economical aspects as well as on donatorś knowledge about breastfeeding was considered necessary. METHODS: 35 donators were interviewed and an experimental investigation was performed with 33 samples of breast milk stored at room temperature (17 masculine C to 30.5 masculine C) and bacteriologically analyzed at zero, three, six and nine hours after collection. The same breast milk was stored at refrigerator (2 masculine C to 6 masculine C) as a control procedure. Total count of bacterial contents and identification of Staphylococcus aureus and Escherichia coli were evaluated.RESULTS: The enterviews revealed the low socio-economical and cultural level of lactating mothers and their little experience in expressing, collecting and using their own milk. Bacteriological data analysis showed mesophyllous average of 7.1x10(3)UFC/mL, acceptable outline of bacterial contamination, despite the use of a simplified hygiene technique. After nine hours, samples stored at room temperature showed final average of bacterial contents similar to the first ones (7.3x10(3)UFC/mL) and without relevant statistic differences from the ones kept under refrigeration (p=0.05) for studied bacterias.CONCLUSION: This study shows that it is possible to use unprocessed breast milk for babýs consumption if it is stored at room temperatures until nine hours after it has been collected. However, mothers have to be told about the possibility of storing breast milk for babies later consumption.

Asymptotic theory for the MLE from randomly censored exponential samples

The MLE of the parameter of the exponential population from the censored observations is considered. The Edgeworth expansions for the Studentized MLE are established by representing the relevant statistic as a U-statistic plus a remainder. A semiparametric bootstrap method is introduced to the random censored model and the accuracy of bootstrap approximation of the MLE is investigated. Furthermore, it is shown that the MLE is asymptotically minimax efficient.

Enumeration of three-dimensional convex polygons

A self-avoiding polygon (SAP) on a graph is an elementary cycle. Counting SAPs on the hypercubic lattice ℤ d withd≥2, is a well-known unsolved problem, which is studied both for its combinatorial and probabilistic interest and its connections with statistical mechanics. Of course, polygons on ℤ d are defined up to a translation, and the relevant statistic is their perimeter.

Birth Weight-specific Mortality for Extremely Low Birth Weight Infants Vanishes by Four Days of Life: Epidemiology and Ethics in the Neonatal Intensive Care Unit

The persistent differences between those who question the appropriateness of aggressive resuscitative measures for many extremely low birth weight (ELBW) infants (birth weight < 1001 g) and those who generally initiate such treatment has been a source of ongoing tension for physicians, parents, judges, and policymakers. We believe that much of this tension may be a result of the way the issue is framed. We began this study with the intuition that although many ELBW infants die, most succumb quickly. Were this true, discussions that considered only survival rates might miss the point. A more relevant statistic might be the degree to which interventions prolong dying, extend suffering, or use resources for infants who will eventually die. We determined the survival and nonsurvival for 429 ELBW infants admitted to our neonatal intensive care unit (NICU) for 3 years. We noted particularly the relationship between birth weight, illness severity (fraction of inspired oxygen [Fio2] requirement for infants requiring mechanical ventilation), and the time course of mortality for nonsurvivors. We next calculated a resource utilization index (NICU bed days occupied by survivors and nonsurvivors) for each patient and for the population as a whole. Finally, we determined how NICU resources were distributed among infants who eventually died and those who survived. Of the 429 ELBW infants alive on day of life (DOL) 1,202 (47%) survived to be discharged. on DOL 1, both birth weight and illness severity independently predicted likelihood of survival. Approximately 80% of ELBW deaths occurred in the first 3 days of life-- consequently, once an infant had survived to DOL 4, the likelihood of survival was dramatically enhanced (81% for the 249 patients alive on DOL 4). In addition, although survival for DOL 4 infants continued to depend on illness severity, survival no longer depended on birth weight. These observations on DOL 4 were confirmed in the subpopulation of 212 infants whose birth weight was < 750 g. Overall, although 53% of ELBW babies admitted died, only approximately 13% of all NICU bed-days (a proxy for resource allocation) were devoted to infants who did not survive. This figure did not vary as a function of birth weight. Generally, when we talk of survival rates to parents, ethics committees, or policy makers, we base our predictions largely on birth weight. The data presented here suggest that predictions should be corrected by including DOL and that, when this is done, the prognostic value of birth weight rapidly diminishes. In addition, birth weight-specific mortality and day of death for nonsurvivors correlated inversely; that is more of the smaller infants died, but the doomed ones died more quickly. Consequently, medical resources allocated to nonsurvivors remained low, and independent of birth weight. This formulation lends weight both to the reasonableness of physicians in offering NICU care to ELBW infants, with unlikely prospects for survival, and of parents and surrogate decision-makers in requesting/ assenting to it.

Prediction intervals for Weibull observations, based on early-failure data

Let n similar components with Weibull lives be put on life-test simultaneously, and let the first r failures be observed. A prediction interval for failure-time X/sub k/, 0<r<k/spl les/n, is constructed. An explicit formula is obtained for computing quantiles of a relevant pivotal statistic. Prediction intervals based on various estimators of parameters and methods are compared. The results can be used to predict the failure-time of a k-out-of-n:F system.

The Use of Word, Phrase and Intent Accuracy as Measures of Connected Speech Recognition Performance

Eleven subjects participated in a study designed to test the accuracy of a newer-generation connected speech recognition system using a 49 word vocabulary likely to be used in an aircraft cockpit environment. The 49 vocabulary words were used to create 392 test phrases. These phrases were divided into three groups: Complex phrases, which contain more than five words, and two groups of Simple phrases, which contain 5 words or less. The simple phrases were divided into Simple Alternate and Simple No-Alternate phrases, depending on whether or not the phrase was the only one in the entire vocabulary capable of carrying out a particular action once recognition occurred. Performance of the recognition system was measured with three accuracy statistics: word accuracy, the most commonly reported statistic in speech recognition research, phrase accuracy, which is gaining popularity in connected speech recognition research, and intent accuracy, which is probably the most relevant statistic that could be reported in research of this type. Significantly different word, phrase, and intent accuracy results were obtained for the three different phrase types.