The exact distribution of the ratio of a linear combination of chi-square variables over the root of a product of chi-square variables

This article gives the exact distribution of a statistic whose numerator and denominator are independent, the former being a linear combination of independent chi-square variables and the latter being the kth root of a product of k independent chi-square variables. This structure appears in the study of multivariate linear functional relationship models. The technique of the inverse Mellin transform is used in order to obtain the density of this test statistic in a computable form.     

Force steadiness in the lower extremities as an independent predictor of functional performance in older women

The relationship between isometric force control and functional performance is unknown. Submaximal steadiness and accuracy were measured during a constant force-matching task at 50% of maximal isometric voluntary contraction (MVC) of the knee extensors in 19 older women (70-89 years). Other variables included MVC, rate of torque development, and EMG activity. Functional performance was assessed during maximal performance of walking endurance, chair rising, and stair climbing. Isometric steadiness (but not accuracy) was found to independently predict chair-rise time and stair-climbing power and explained more variance in these tasks than any other variable. Walking endurance was related to muscle strength but not steadiness. These results suggest that steadiness is an independent predictor of brief, stressful functional-performance tasks in older women with mild functional impairment. Thus, improving steadiness might help reduce functional limitations or disability in older adults.     

Improving quality of life after breast cancer: prevention of other diseases

Many women with breast cancer will be diagnosed at an early stage through screening programmes. Furthermore, most women affected by breast cancer will not die from it but from other diseases, owing to recent improvements in treatment. This article assesses whether breast cancer survivors suffer more frequently from other diseases. Specifically, it examines whether they have a higher incidence of other cancers, cardiovascular events and osteoporotic fractures. Women with breast cancer and three or more co-morbid conditions have a 20-fold higher rate of mortality from causes other than breast cancer and a 4-fold higher rate of all-cause mortality when compared with patients who have none. Breast cancer survivors are at increased risk of other cancers, such as stomach, colorectal and lung. Radiotherapy, trastuzumab and aromatase inhibitors increase the risk of cardiovascular disease. However, tamoxifen does not, although it is associated with an increased risk of venous thromboembolism. Aromatase inhibitors, but not tamoxifen, increase the risk of osteoporotoic fracture and bisphosphonate therapy should be considered.     

The curse of hope

In K?szegi and Rabin’s (Q J Econ 1133–1165, 2006, Am Econ Rev 97:1047–1073, 2007) reference-dependent model of preferences, the chance of obtaining a better outcome can reduce an agent’s expected utility through an increase in the stochastic reference point. This means that individuals may prefer stochastically dominated lotteries. In this sense, hope, understood as a small probability of a better outcome, can be a curse. While K?szegi and Rabin focus on a linear specification of the utility function, we show that this effect occurs more broadly. Using fairly plausible assumptions and parameter values, we specify the conditions under which it occurs, as well as the type of lotteries in which this should be expected. We then show that while a simple subjective transformation of probability into weights of the reference point may in some cases mitigate the issue, in others, it can intensify it or even generate new ones. Finally, we extend the model by adding the individual’s current reference point (status quo) to the stochastic reference point. We show that this modification can reconcile K?szegi and Rabin’s model with the apparent empirical infrequency of stochastically dominated choices while maintaining its main qualitative results.     

On the distribution of linear combinations of the components of a Dirichlet random vector

On making use of a result of Imhof, an integral representation of the distribution function of linear combinations of the components of a Dirichlet random vector is obtained. In fact, the distributions of several statistics such as Moran and Geary's indices, the Cliff‐Ord statistic for spatial correlation, the sample coefficient of determination, F‐ratios and the sample autocorrelation coefficient can be similarly determined. Linear combinations of the components of Dirichlet random vectors also turn out to be a key component in a decomposition of quadratic forms in spherically symmetric random vectors. An application involving the sample spectrum associated with series generated by ARMA processes is discussed.     

Gender, household labor, and scholarly productivity among university professors

In the present paper, we use data collected from 673 faculty members at one research university to describe the division of household labor among academics and explore the relationship between household labor and scholarly productivity. The analyses demonstrate that domestic labor is distributed along relatively traditional lines among academics, reflecting the continued traditionalism found in the general population regarding house-hold labor and child care. Women college-professors shoulder considerably more house-hold labor than do their male colleagues—particularly when they are married and when there are children in the home. We hypothesized that the gender discrepancies in house-hold labor we found would translate into differences in scholarly productivity; however, this was the case only among tenure-track faculty with children in the home. This work was completed while the authors were supported by a grant from the National Institute on Aging (RO1 AG18869-01, Jill Suitor and Karl Pillemer, Principal Investigators). The data collection was funded by the Louisiana State University Commission on the Status of Women.     

Intra-rater reliability of hip abductor isometric strength testing in a standing position in older fallers and non-fallers

Background

Reduced hip muscle strength has been shown to be a major factor related to falls in older persons. However, comprehensive assessment of hip abduction strength in the clinical setting is challenging. The aim of this study was to investigate the feasibility and intra-rater reliability of a quick and simple hip abductor strength test in a functional standing position.

Methods

Individuals over 65 years of age were recruited from the geriatric department of a university hospital and an outpatient clinic. Thirty-two older subjects, including 16 fallers (≥1 fall during the last 12 months) and 16 non-fallers were included. Maximum voluntary isometric strength (MVIS) and rate of force generation (RFG) of the hip abductors of the right leg were evaluated in a standing position using a hand-held dynamometer. Two test-sessions were carried out. All hip strength values were normalized to participants’ weight. Reliability was determined using the intra-class correlation coefficient agreement (ICC_agreement), the standard error of measurement (SEM) and a Bland and Altman analysis (BA).

Results

All participants completed the strength tests, which took a mean 2.47?±?0.49 min (one limb). Intra-rater reliability was higher for MVIS (0.98_{[0.95–0.99]}) than RFG (ICC?=?0.93_{[0.87–0.97]}) for the entire sample. In the non-fallers, ICC was 0.98_{[0.95–1.00]} (SEM?=?0.08 N.kg^??1) for MVIS and 0.88_{[0.75–0.96]} for RFG (SEM?=?1.34 N.kg^-1.s^-1). In the fallers, ICC was 0.94_{[0.89–0.98]} (SEM?=?0.11 N.kg^??1) for MVIS and 0.93_{[0.84–0.98]} (SEM?=?1.12 N.kg^??1.s^??1) for RFG. The BA plot showed that the MVIS and RFG values did not differ across test-sessions, showing that no learning effect occurred (no systematic effect). The mean differences between test-sessions were larger and the LOA smaller in the fallers than in the non-fallers.

Conclusion

Assessment of hip strength in a standing position is feasible, rapid and reliable. We therefore recommend this position for clinical practice. Future studies should investigate the diagnostic value of hip abductor strength in standing to discriminate between fallers and non-fallers, and to determine if change in strength following a falls prevention program reduces the risk of falls.

     

Burnout and Mental Health in Swiss Vocational Students: The Moderating Role of Physical Activity

Few studies have focused on burnout among vocational students. This study examined the association between burnout and mental health among 56 Swiss vocational students (29 males, 27 females, M = 18.1, SD = 1.2 years) and tested whether recommended levels of moderate‐to‐vigorous physical activity (MVPA) attenuate this relationship. Burnout was strongly associated with increased depressive symptoms and decreased levels of life satisfaction, mental toughness, and quality of sleep. Students above recommended levels of MVPA reported lower burnout and higher mental health. No significant moderator effects were observed. Symptoms of burnout were associated with increased mental health problems. Physical activity should be promoted to prevent burnout, because nearly half of the students did not meet MVPA recommendations.     

Impact of the Format,Arrangement and Availability of Electronic Gaming Machines Outside Casinos on Gambling

Abstract

This study evaluates the influence of the format, arrangement and availability of Electronic Gaming Machines Outside Casinos (EGMOC) on gambling behaviour and perceptions. Two studies comprising occasional, at-risk and probable pathological gamblers were conducted. The first study used focus groups, while the second was conducted in a laboratory setting reproducing a bar. The results of the former study indicate that while format does not influence gambling behaviours, the arrangement of EGMOC in a gambling setting is a critical factor: in general, gamblers perceive isolated areas in a gambling venue as a factor contributing to impaired control. However, behavioural results obtained in the laboratory setting do not corroborate subjective data. Finally, gamblers suggested almost unanimously that the availability of EGMOC should be limited to a small number of sites. The results are discussed in the perspective of responsible gambling policies.