Calcular e apresentar tamanhos do efeito em trabalhos científicos (1): As limitações do p < 0,05 na análise de diferenças de médias de dois grupos

A Revista Portuguesa de Investigação Comportamental e Social exige que os autores sigam as recomendações do Publication Manual of the American Psychological Association (APA, 2010) na apresentação da informação estatística. Uma das recomendações da APA é de que os tamanhos do efeito sejam apresentados associados aos níveis de significância estatística. Uma vez que os valores de p decorrentes dos resultados dos testes estatísticos não informam sobre a magnitude ou importância de uma diferença, devem então reportar-se os tamanhos do efeito (TDE). De facto, os TDE dão significado aos testes estatísticos, enfatizam o poder dos testes estatísticos, reduzem o risco de a mera variação amostral ser interpretada como relação real, podem aumentar o relato de resultados “não-significativos” e permitem acumular conhecimento de vários estudos usando a meta-análise. Assim, os objetivos deste artigo são os de apresentar os limites do nível de significância; descrever os fundamentos da apresentação dos TDE dos testes estatísticos para análise de diferenças entre dois grupos; apresentar as fórmulas para calcular os TDE, fornecendo exemplos de estudos nossos; apresentar procedimentos de cálculo dos intervalos de confiança; fornecer as fórmulas de conversão para revisão da literatura; indicar como interpretar os TDE; e ainda mostrar que, apesar de frequentemente ser interpretável, o significado (efeito pequeno, médio ou grande para uma métrica arbitrária) pode ser impreciso, havendo necessidade de ser interpretado no contexto da área de investigação e de variáveis do mundo real

MCBT: Multi-Hop Cluster Based Stable Backbone Trees for Data Collection and Dissemination in WSNs

We propose a stable backbone tree construction algorithm using multi-hop clusters for wireless sensor networks (WSNs). The hierarchical cluster structure has advantages in data fusion and aggregation. Energy consumption can be decreased by managing nodes with cluster heads. Backbone nodes, which are responsible for performing and managing multi-hop communication, can reduce the communication overhead such as control traffic and minimize the number of active nodes. Previous backbone construction algorithms, such as Hierarchical Cluster-based Data Dissemination (HCDD) and Multicluster, Mobile, Multimedia radio network (MMM), consume energy quickly. They are designed without regard to appropriate factors such as residual energy and degree (the number of connections or edges to other nodes) of a node for WSNs. Thus, the network is quickly disconnected or has to reconstruct a backbone. We propose a distributed algorithm to create a stable backbone by selecting the nodes with higher energy or degree as the cluster heads. This increases the overall network lifetime. Moreover, the proposed method balances energy consumption by distributing the traffic load among nodes around the cluster head. In the simulation, the proposed scheme outperforms previous clustering schemes in terms of the average and the standard deviation of residual energy or degree of backbone nodes, the average residual energy of backbone nodes after disseminating the sensed data, and the network lifetime

Sharing in a Privately Owned Workstation Environment

Private workstations interconnected by networks have become widely available as sources of computing cycles. Each workstation is typically owned by a single user in order to provide a high quality of service for the owner. In most cases, an owner does not have computing demands as large as the capacity of the workstation. Therefore, most of the workstations are often under utilized. Nevertheless, some users have demands that exceed the capacities of their workstations. The desire to satisfy the requirements of users who need extra capacity without lowering the quality of service of owners of under utilized workstations raises the following challenging question: Can we provide a high quality of service in a highly utilized workstation cluster? The problem identified by this question is how to share workstation capacity with minimal interferencewith the local activity of workstation owners. This thesis addresses this problem of capacity sharing by exploring issues involved with the formation of a processor from a workstation cluster. The capacity of the processor bank comes from the donation of workstations during periods that the stations are not used During periods of usage, the workstations are withdrawn from the processor bank. We examined the amount of capacity available for donation, and the characteristics of the donation and withdrawal periods. A desig

Analytical Markovian Model of TCP Congestion Avoidance Algorithm Performance

We consider the performance of the TCP congestion avoidance algorithm by developing the Markovian model of the flow control algorithm, often referred to as Additive Increase Multiplicative Decrease. Analytically, we evaluate the steady state distributions of the congestion window size and the throughput. Further processing of the distributions yields moment of any degree i.e. expectation, variance, quantiles and other important performance metrics. Our model covers a wide range of networking environments. It relaxes several important restrictions presently accepted in analytical studies of TCP. Besides strict application in design and engineering, the model states usability bounds for simple estimations of the average TCP throughput. The paper includes a set of numerical examples that illustrate the scope of the model and state important properties of congestion avoidance. Our results are validated by experimental analysis. The values generated by the model are compared to that demonstrated by TCP connections in an emulated network environment and by other published models as well. The model demonstrates high stability and good agreement with the experiments

Improving the Operation Efficiency of Supermedia Enhanced Internet Based Teleoperation via an Overlay Network

Abstract — For Internet based real-time teleoperation systems, random time delay can cause instability in the closed loop control system and hence hinder task accomplishment. Event based control systems have been proposed to overcome the instability caused by the random time delay. High latency at the transport layer can still impede effective and reliable execution of tasks with high dexterity requirements. Network QoS based dynamic resource allocation has been proposed to increase the efficiency and reliability of task execution. However, these approaches only try to mitigate or overcome the effects of random time delay and do not address the cause of latency issues in the communication channel. This paper addresses the efficiency and reliability requirements for supermedia enhanced teleoperated systems by reducing the end-to-end transmission latency through the use of overlay networks. The proposed system reduces the transmission latency by using multiple, disjoint paths in overlay networks. The proposed system facilitates reliable and efficient task completion for tasks with high dexterity requirements. Experimental validation of the proposed teleoperated system using the PlanetLab Network is provided for the task of teleoperating a mobile manipulator system

Mobile Peer Membership Management to Support Multimedia Streaming

A CHUM (Cooperating ad Hoc networking to sUpport Messaging) network is an ad hoc network in which mobile devices cooperate to reduce connection costs when accessing wireless global networks. We study how members of a CHUM network cooperate in order to download multimedia data, such as on-air TV programs. Each peer in a CHUM takes turns serving as a proxy, which makes an Internet connection and downloads multimedia data for the other members. Then, the proxy distributes the data to other peers using its ad hoc connection, which we call chumcast. The proxy maintains and updates peer membership information and determines the next CHUM proxy. The CHUM network includes a recovery procedure when a proxy fails or when a CHUM network partitions