Sample size calculations for clinical studies allowing for uncertainty about the variance

One of the most important steps in the design of a pharmaceutical clinical trial is the estimation of the sample size. For a superiority trial the sample size formula (to achieve a stated power) would be based on a given clinically meaningful difference and a value for the population variance. The formula is typically used as though this population variance is known whereas in reality it is unknown and is replaced by an estimate with its associated uncertainty. The variance estimate would be derived from an earlier similarly designed study (or an overall estimate from several previous studies) and its precision would depend on its degrees of freedom. This paper provides a solution for the calculation of sample sizes that allows for the imprecision in the estimate of the sample variance and shows how traditional formulae give sample sizes that are too small since they do not allow for this uncertainty with the deficiency being more acute with fewer degrees of freedom. It is recommended that the methodology described in this paper should be used when the sample variance has less than 200 degrees of freedom.     

Over-education and Gender Occupational Differences in Spain

This paper explores the role of over-education in shaping the negative relationship between the education level attained by employees and the fact of working in a gender-dominated occupation, in Spain, a country where the phenomenon of over-education is common. Applying multinomial logit regressions, and controlling for individual and job characteristics, the results confirm the typical finding that having a university degree decreases the odds of working in a gender-dominated occupation. However, this is only true in the case of women when considering long—more than 3 years—university studies. The evidence also suggests that the general spread of over-education in Spain weakens that relationship so that reducing over-education would eventually lead to more uniformity in the gender-distribution of employment across occupations.

     

Elite players’ perceptions of football playing surfaces: a mixed effects ordinal logistic regression model of players’ perceptions

The aim of this study was to determine potential explanatory factors that may be associated with different attitudes amongst the global population of elite footballers to the use of different surfaces for football. A questionnaire was used to capture elite football players’ perceptions of playing surfaces and a mixed effects ordinal logistic regression model was used to explore potential explanatory factors of players’ perceptions. In total, responses from 1129 players from 44 different countries were analysed. The majority of players expressed a strong preference for the use of Natural Turf pitches over alternatives such as Artificial Turf. The regression model, with a players’ country as a random effect, indicated that players were less favourable towards either Natural Turf or Artificial Turf where there was perceived to be greater variability in surface qualities or the surface was perceived to have less desirable properties. Player’s surface experience was also linked to their overall attitudes, with a suggestion that the quality of the Natural Turf surface players experienced dictated players’ support for Artificial Turf.     

Bimodal Birnbaum–Saunders distribution with applications to non negative measurements

In this article, we introduce a new extension of the Birnbaum–Saunders (BS) distribution as a follow-up to the family of skew-flexible-normal distributions. This extension produces a family of BS distributions including densities that can be unimodal as well as bimodal. This flexibility is important in dealing with positive bimodal data, given the difficulties experienced by the use of mixtures of distributions. Some basic properties of the new distribution are studied including moments. Parameter estimation is approached by the method of moments and also by maximum likelihood, including a derivation of the Fisher information matrix. Three real data illustrations indicate satisfactory performance of the proposed model.     

Moral education as intercultural moral education

In a diverse country such as Peru, moral education should reflect social, cultural, political and spiritual dilemmas of both indigenous and non-indigenous peoples and their communities. To promote understanding and respect amongst people from different sociocultural backgrounds, moral education should encourage a dialogue between indigenous values and mainstream hegemonic values. In this article, we argue for the need to conceptualise moral education as intercultural. Against a common view that portraits indigenous people as incommensurable, that is, as trapped in their own radically different moral perspective, our own research in Shipibo-Konibo and Asháninka communities show that indigenous people display a moral point of view when analysing cultural traditions and practices. This moral point of view appears intertwined with their cultural values and ethnic identities and allows intercultural dialogue. In this vein, we argue for the need to incorporate intercultural moral conflicts and dilemmas into moral education to promote understanding and respect for others.     

PRICES,INFLATION, AND SMOKING ONSET: THE CASE OF ARGENTINA

This article examines the effect of tobacco prices on the decision to start smoking in Argentina. Argentina is an interesting case to explore given its high smoking rates, its recent experience with periods of very high and hyperinflation, and the mixed evidence of the effect of prices on smoking onset, particularly in low‐ and middle‐income countries. We used data from four cycles of two large national surveys conducted between 2005 and 2011 and discrete‐time hazard models. We found that tobacco prices had a statistically significant and fairly large impact on the hazard of smoking onset, and these findings were robust to alternative specifications. We also found that prices had little effect on the hazards of smoking onset during periods of hyper‐ and very high inflation, which provide some support for the notion that prices lose their informational role in such periods. Governments need to be cognizant that their most important policy tool to reduce tobacco use—taxes that increase real tobacco prices—is likely no longer effective during these times. (JEL C41, H20, I12, I18)     

Variations in Child Care by Grandparents During the First Three Years

Routine child care by grandparents was examined for 1,229 children who were participants in the National Institute of Child Health and Human Development (NICHD) Study of Early Child Care. Four groups were identified: extended full‐time care, extended part‐time care, sporadic care, and no routine care during the first three years. The odds of sporadic child care by grandparents were higher when mothers were relatively young and worked nonstandard hours. The odds of extended full‐time grandparent care versus extended part‐time grandparent care were higher for mothers of color and mothers with more extensive full‐time employment. All types of grandparent care were more likely when a grandparent lived in the household. These findings suggest that grandparent care is heterogeneous and may occur in response to different family circumstances.     

Barriers to accessing HIV and sexual health services among gay men in Tasmania,Australia

We examined barriers to accessing HIV and sexual health services among gay and bisexual men (GBM) in Tasmania, Australia, using in-depth interviews. Most participants were satisfied with the care they had received at public sexual health services. Barriers included the limited number of services, concerns about anonymity and privacy in small communities, difficulties accessing services via a general practitioner, and perceived stigma and discrimination. Improving the accessibility and availability of HIV and sexual health services in Tasmania is crucial to promote the engagement of GBM, which could be achieved via combined efforts of government services and community organizations.