Nonparametric multivariate rank tests and their unbiasedness

Although unbiasedness is a basic property of a good test, many tests on vector parameters or scalar parameters against two-sided alternatives are not finite-sample unbiased. This was already noticed by Sugiura [Ann. Inst. Statist. Math. 17 (1965) 261--263]; he found an alternative against which the Wilcoxon test is not unbiased. The problem is even more serious in multivariate models. When testing the hypothesis against an alternative which fits well with the experiment, it should be verified whether the power of the test under this alternative cannot be smaller than the significance level. Surprisingly, this serious problem is not frequently considered in the literature. The present paper considers the two-sample multivariate testing problem. We construct several rank tests which are finite-sample unbiased against a broad class of location/scale alternatives and are finite-sample distribution-free under the hypothesis and alternatives. Each of them is locally most powerful against a specific alternative of the Lehmann type. Their powers against some alternatives are numerically compared with each other and with other rank and classical tests. The question of affine invariance of two-sample multivariate tests is also discussed.Comment: Published in at http://dx.doi.org/10.3150/10-BEJ326 the Bernoulli (http://isi.cbs.nl/bernoulli/) by the International Statistical Institute/Bernoulli Society (http://isi.cbs.nl/BS/bshome.htm

Sharply Orthocomplete Effect Algebras

Special types of effect algebras $E$ called sharply dominating and S-dominating were introduced by S. Gudder in \cite{gudder1,gudder2}. We prove statements about connections between sharp orthocompleteness, sharp dominancy and completeness of $E$. Namely we prove that in every sharply orthocomplete S-dominating effect algebra $E$ the set of sharp elements and the center of $E$ are complete lattices bifull in $E$. If an Archimedean atomic lattice effect algebra $E$ is sharply orthocomplete then it is complete

A Model of Digital Payment Infrastructure Formation and Development: The EU Regulator´s Perspective

The payment field is being rapidly transformed. New players have emerged and are threatening the well-established positions of the incumbents. This process is driven by technology change and market forces, and it is shaped by the increasing role of the regulator. When considering the change in the regulatory environment and combining it with the disruptive and innovative nature of the mobile phone, the result is a market that is rapidly transforming from well-established structure into a state of flux. We build a model to understand and explain this transformation of the digital payment infrastructure. The model captures the formation and development of the digital payment infrastructure with a particular emphasis on the regulator´s and innovator’s perspective. It consists of four stages characterized by slow incremental change which are followed by short and rapid bursts of discontinuity. Each stage is portrayed by its evolutionary dynamics, the nature of the payment platform, the legal implications, the level of competition, and what drives the discontinuity. Keywords: digital payments, multi-sided platform, EU payment regulation, digital infrastructures

DIMENSIONALITY REDUCTION METHODS FOR BIOMEDICAL DATA

The aim of this paper is to present basic principles of common multivariate statistical approaches to dimensionality reduction and to discuss three particular approaches, namely feature extraction, (prior) variable selection, and sparse variable selection. Their important examples are also presented in the paper, which includes the principal component analysis, minimum redundancy maximum relevance variable selection, and nearest shrunken centroid classifier with an intrinsic variable selection. Each of the three methods is illustrated on a real dataset with a biomedical motivation, including a biometric identification based on keystroke dynamics or a study of metabolomic profiles. Advantages and benefits of performing dimensionality reduction of multivariate data are discussed

Introducing Platform Interactions Model for Studying Multi-Sided Platforms

Multi-Sided Platforms (MSPs) function as socio-technical entities that facilitate direct interactions between various affiliated to them constituencies through developing and managing IT architecture. In this paper, we aim to explain the nature of the platform interactions as key characteristic of any MSP. To this end, we propose the Platform Interaction Model (PIM), built upon Activity Theory and Business Action Theory. We then test its explanatory capability by applying it to four cases. Based on our analysis, we argue that MSPs enable various types of interactions, which has implications for the initial adoption, competitiveness, and subsequent expansion of particular MSP

Introducing Reach And Range For Digital Payment Platforms

Numerous digital payment solutions, which rely on new disruptive technologies, have been launched on the payment market in the recent years. But despite the growing number of mobile payment apps, very few solutions turn to be successful as the majority of them fail to gain a critical mass of users. In this paper we investigate two successful digital payment solutions in order to outline some of the factors which contribute to the widespread adoption of a digital payment platform. In order to conduct our analysis we propose the Reach and Range Framework for Multi-Sided Platforms. Our study indicates that the success of digital payment platforms lies with the ability of the platform to balance the reach (number of participants) and the range (features and functionalities) of the platform

A Typology of Multi-sided Platforms: The Core and the Periphery

In this paper we address how the composition of a platform impacts the platform’s business model. By platform’s business model we mean platform features, platform architecture and platform governance. To this end, we construct the Platform Business Model Framework. We apply the framework to three exemplary cases which allow us to illustrate the platform heterogeneity and to support new MSPs typology. As examples we include a physical two-sided platform (Gatwick Airport) that adds a third side, a digital one-sided platform transformed into being two-sided (Pingit) and a digital one-sided platform which evolved several steps into being multi-sided (Facebook). Our analysis shows a structural difference between one-sided, two-sided and multi-sided platforms and that platforms consist of a core and potentially also a periphery. The sides of a platform and the ties which connect them can be arranged in several configurations. The particular platform architecture can explain the difficulties in designing a viable business models for platforms

PLATFORM CONSTELLATIONS: THE CASE OF KAKAOTALK AND LINE

This research paper presents an initial attempt to introduce and explain the emergence of new phenomenon, which we refer to as platform constellations. Functioning as highly modular systems, the platform constellations are collections of highly connected platforms which co-exist in parallel and as such allow us to study platforms not only as separate entities, but also to investigate the relationship between several platforms offered and governed by one and the same platform provider. By investigating two case studies of indigenous platform constellations formed around the hugely popular instant messaging apps KakaoTalk and LINE, we are able to gain valuable insights about the nature of these new constructions and to capture and synthesize their main characteristics in a framework. Our results show that platform constellations possess unique innovative capabilities, which can improve users’ acquisition and users’ engagement rates as well as unlock new sources of value creation and diversify revenue streams

Strength training and changes in the dynamics of running economy

The aim of this study was to examine an acute effect of 4RM training and plyometric training (PT) on running economy (RE; O2 consumption) in endurance runners during a 48 hour interval. Eight performance runners (age 25.4±1.4 years) completed a maximum strength training (4RM) of lower limbs (3 sets, rest 2 min, 5 exercises) and subsequently underwent a RE test on a treadmill (speed 8, 10 and 12 km·h-1) at three time intervals (0, +24 and +48 h) after the training. We found that the average VO2·BM-1·min-1 and ΔVO2·BM-1·min-1 at the given speed increased from baseline (a pretest 48 h before the strength intervention) by 2.3-5.6% and culminated after 24 h. These changes in RE after the strength intervention were not statistically significant, when compared to the pretest (48 h before the intervention). The second investigation was conducted in seven runners (age 25±1.6 years). This time the intervention was plyometric (7 sec load, rest 2 min, maximum intensity, 3 sets, 6 exercises on the dominant lower limb). We found that the average VO2·BM-1·min-1 and ΔVO2·BM-1·min-1 at given speeds at intervals 0, +24 and +48 h did not increase, when compared to the pretest (p < 0.05; max +1%). These minimal changes probably resulted from the design of the PT, which had not a sufficiently destructive effect on muscle cells. The comparison of these two investigations indicates a stronger (although statistically insignificant) deterioration of RE after 4RM training versus PT.This investigation was conducted within the framework of a specific students’ research at the Masaryk University 0790/2012 "Factors affecting the economy of running (the effect of explosive strength training and stretching acutely applied before performance on the economy of running) II"

The running economy difference between running barefoot and running shod

Barefoot (BF) running is very popular topic among runners and coaches, and very often discussed in papers and even mass-media point is health aspect. The aim of this study is verify influence BF on physiological indicators. Nine women (age 21.1 ± 1.79 y.o., weight 59.7 ± 5.86 kg, height 164.8 ± 4.02 cm, no previous BF running experience, athletes, non-runners) completed two tests of running economy (RE) in minimal gap of 48 hours. Test of RE consisted of dynamic stretching warm-up and 7 minutes run on treadmill (constant velocity 7 km·h-1, inclination +1 %) BF and shoed (RS). Hearth rate (HR; beats·min-1) and oxygen uptake (RE, running economy; ml·kg-1·min-1) were collected in last two minutes of each test. There were found insignificant differences (α = .05) in HR (BF 160.92 ± 22.62 vs. RS 163.5 ± 20.99; p = .214) a RE (BF 31.5 ± 2.65 vs RS 30.21 ± 2.91; p = .086). There were been discovered seven individual lower values of RE in BF, as well as same number of lower values of HR (BF). Running barefoot is insignificant economical in among non-experienced barefoot women athletes.This investigation was conducted within the framework of a specific students’ research at the Masaryk University 0867/2013 "Factors affecting the economy of running 3"