Kinematics used by world class tennis players to produce high-velocity serves

The purpose of this study was to quantify ranges and speeds of movement, from shoulder external rotation to ball impact, in the tennis service actions of world class players. Two electronically synchronised 200 Hz video cameras were used to record 20 tennis players during singles competition at the Sydney 2000 Olympic games. Three-dimensional motion of 20 landmarks on each player and racquet were manually digitized. Based upon the mean values for this group, the elbow flexed to 104 degrees and the upper arm rotated into 172 degrees of shoulder external rotation as the front knee extended. From this cocked position, there was a rapid sequence of segment rotations. The order of maximum angular velocities was trunk tilt (280 degrees/s), upper torso rotation (870 degrees/s), pelvis rotation (440 degrees/s), elbow extension (1510 degrees/s), wrist flexion (1950 degrees/s), and shoulder internal rotation. Shoulder internal rotation was greater for males (2420 degrees/s) than females (1370 degrees/s), which may be related to the faster ball velocity produced by the males (50.8 m/s) than the females (41.5 m/s). Although both genders produced segment rotations in the same order, maximum upper torso velocity occurred earlier for females (0.075 s before impact) than for males (0.058 s). At impact, the trunk was tilted 48 degrees above horizontal, the arm was abducted 101 degrees and the elbow, wrist, and lead knee were slightly flexed. Male and female players should be trained to develop the kinematics measured in this study in order to produce effective high-velocity serves.     

Avoiding the perils and fulfilling the promises of microfinance: A closer examination of the educational outcomes of clients’ children in Nicaragua

Many microfinance advocates claim that micro-credit has a positive effect on the educational outcomes of the children of micro-credit borrowers, and that these educational improvements provide us with evidence that micro-credit institutions are serving the social function for which they have been designed. This paper draws attention to this area of microfinance-impact research, and explores the promises and perils associated with the impact of microfinance on children's educational outcomes. The goal of this discussion is to ensure that the pervasive spread of microfinance to all parts of the globe is accompanied by benefits to children's educational outcomes. Drawing on the research we conducted in Nicaragua in 2008, we, the joint authors of this paper share insights that we hope can help to upgrade the practices currently being employed by both microfinancers and children's educational institutions, and to thereby strengthen academic-credit linkages within client households.     

Development and validation of the groupwork skills questionnaire (GSQ) for higher education

The aim of the present study was to develop and provide psychometric evidence in support of the groupwork skills questionnaire (GSQ) for measuring task and interpersonal groupwork skills. A 46-item version of the GSQ was initially completed by 672 university students. The number of items was reduced to 15 following exploratory factor analyses, and a two-factor model consisting of task and interpersonal groupwork skills was revealed. Confirmatory factor analyses with model re-specification on new data (n = 275 students) established that the best fitting model consisted of 10 items and the same two factors (task and interpersonal). Concurrent validity of the GSQ was then determined with 145 participants by demonstrating significant relationships (p < 0.05) with attitudes towards groupwork and groupwork self-efficacy. Test–retest reliability was examined over a one-week interval. Overall, the GSQ demonstrates good validity and reliability, and has potential for both research and pedagogical application.     

Science in the early Athenaeum: a mirror of crystallization

The Athenaeum, one of the most influential weekly magazines of Victorian Britain, was launched in 1828, towards the end of the period which saw the crystallization of science out of eighteenth-century natural philosophy and the differentiation of the individual sciences one from another. We examine the magazine's coverage of specific scientific areas in the year from May 1828 to April 1829, looking at what it defined as science and how it arrived at its definitions. The picture that emerges is complex, influenzed by editorial preferences as well as more clearly discernible objective criteria. But, at this stage, The Athenaeum appears to be opposed to opening up a gulf between the scientifically literate and the rest of its readership, reminding science of its debt to earlier endeavours.     

Classroom behavioral interventions: Do teachers consider the function of the behavior?

Teachers and school psychologists are often involved in designing classroom behavioral interventions. Functional behavioral assessment, mandated under certain circumstances by IDEA (1997), is considered a best practices approach in designing behavioral interventions. A functional assessment can result in an intervention tailored to a specific student's needs. The purpose of this study was to determine whether teachers considered the function of a behavior when determining a classroom intervention. A sample of 209 Kentucky teachers were given scenarios of students exhibiting problematic behaviors. Information was provided so that the function of the behavior was apparent. The results found that few teachers considered the behavioral function when deciding upon an intervention. Few differences were found between regular and special education teachers. Implications for school psychologists are discussed. © 2000 John Wiley & Sons, Inc.     

Population Invariance and the Equatability of Tests: Basic Theory and The Linear Case

How does the fact that two tests should not be equated manifest itself? This paper addresses this question through the study of the degree to which equating functions fail to exhibit population invariance across subpopulations. Equating fimctions are supposed to be population invariant by definition. But, when two tests are not equatable, it is possible that the linking functions, used to connect the scores of one to the scores of the other, are not invariant across different populations of examinees. While no acceptable equating function is ever completely population invariant, in the situations where equating is usually performed we believe that the dependence of the equating function on the population used to compute it is usually small enough to be ignored. We introduce two root‐mean‐square difference measures of the degree to which the functions used to link two tests computed on different subpopulations differ from the linking function computed for the whole population. We also introduce the system of “parallel‐linear” linking functions for multiple subpopulations and show that, for this system, our measure of population invariance can be computed easily from the standardized mean differences between the scores of the subpopulations on the two tests. For the parallel‐linear case, we develop a correlation‐based upper bound on our measure that holds for all systems of subpopulations. We illustrate these ideas using data from the SAT I and from a concordance study of several combinations of ACT and SAT I scores, In the appendices, we give some theoretical results bearing on the other equating “requirements” of “same construct,”“same reliability” and one aspect of Lord's concept of equity.     

Intertrial interval effects in pavlovian serial feature positive discriminations

The effects of the intertrial interval (ITI) on learning and performance in Pavlovian appetitive serial feature positive (SFP) discriminations were examined in three experiments with rats. With longer ITIs, acquisition was more rapid, and there was less transfer of the feature’s behavioral control to a separately trained target cue, suggesting that longer ITIs encouraged the use of an occasion setting strategy. Behavior was also affected by discrimination-specific ITIs. Rats were trained with two SFP discriminations. The overall ITI was held constant, but the intervals between trials of one discrimination were varied by intermixing different numbers of trials from the other discrimination. Learning was more rapid when the intervals between trials of a single discrimination were longer. A sequential analyses showed that performance on a trial was impaired when it was preceded by a trial that included the same target cue but with the opposite trial outcome. The results are discussed in the frameworks of proactive interference effects and deletion-comparator processes (Cooper, Aronson, Balsam, & Gibbon, 1990.)