Sample size and power estimation for studies with health related quality of life outcomes: a comparison of four methods using the SF-36

We describe and compare four different methods for estimating sample size and power, when the primary outcome of the study is a Health Related Quality of Life (HRQoL) measure. These methods are: 1. assuming a Normal distribution and comparing two means; 2. using a non-parametric method; 3. Whitehead's method based on the proportional odds model; 4. the bootstrap. We illustrate the various methods, using data from the SF-36. For simplicity this paper deals with studies designed to compare the effectiveness (or superiority) of a new treatment compared to a standard treatment at a single point in time. The results show that if the HRQoL outcome has a limited number of discrete values (< 7) and/or the expected proportion of cases at the boundaries is high (scoring 0 or 100), then we would recommend using Whitehead's method (Method 3). Alternatively, if the HRQoL outcome has a large number of distinct values and the proportion at the boundaries is low, then we would recommend using Method 1. If a pilot or historical dataset is readily available (to estimate the shape of the distribution) then bootstrap simulation (Method 4) based on this data will provide a more accurate and reliable sample size estimate than conventional methods (Methods 1, 2, or 3). In the absence of a reliable pilot set, bootstrapping is not appropriate and conventional methods of sample size estimation or simulation will need to be used. Fortunately, with the increasing use of HRQoL outcomes in research, historical datasets are becoming more readily available. Strictly speaking, our results and conclusions only apply to the SF-36 outcome measure. Further empirical work is required to see whether these results hold true for other HRQoL outcomes. However, the SF-36 has many features in common with other HRQoL outcomes: multi-dimensional, ordinal or discrete response categories with upper and lower bounds, and skewed distributions, so therefore, we believe these results and conclusions using the SF-36 will be appropriate for other HRQoL measures

Physical activity, weight status and diet in adolescents: are children meeting the guidelines?

Childhood obesity is on the increase and maintaining regular physical activity and consuming a healthy diet have become essential tools to combat the condition. The United Kingdom government has recommended guidelines for optimal levels of diet and activity in children. The aim of this paper is to describe and compare self-reported physical activity levels, diet, and Body Mass Indices (BMI) amongst adolescent children, aged 11-15, in the South West (SW) and North West (NW) regions of England and to see if these children were meeting the current targets for optimal levels of: physical activity; fruit/vegetable consumption; fat consumption and BMI. We report the results of a cross-sectional survey of four secondary schools and 1,869 children using the self-reported Western Australian Child and Adolescent Physical Activity and Nutrition Survey (CAPANS) physical activity instrument and a food intake screener questionnaire, in summer and winter. We found that 25% (469/1869) 95% CI: 23% to 27%, of children engaged in 60 minutes of moderate to vigorous physical activity per day; 53% (995/1866) 95% CI: 51% to 56%, took 5 portions of fruit and vegetables per day; while 22% (407/1861) 95% CI: 20% to 24% consumed recommended amount of fats, and 23.7% (276/1164) 95% CI: 21% to 26%, of pupils were obese or overweight as classified by their BMI. Self reported physical activity in young people regardless of area is lower than previously reported and the lack of students engaging in 60 minutes moderate to vigorous activity could have serious public health consequences. If sustained, this could lead to more overweight adults, and more ill health

Physical activity among adolescents and barriers to delivering physical education in Cornwall and Lancashire, UK: a qualitative study of heads of PE and heads of schools. BMC Public Health Journal 2008 Aug 1;8:273.

BACKGROUND: Recent initiatives have been introduced by the UK government into secondary schools to increase pupils' access to physical activity (PA). Despite this, not enough is known about pupils' levels of physical activity or whether the delivery of these initiatives in schools facilitates or creates a barrier for pupils' PA. The aim of this study was to gain an understanding of adolescents PA levels from the perspective of those responsible for delivering physical education (PE) in schools; heads of PE (HOPE) and heads of school (HS). METHODS: Seventeen semi-structured qualitative interviews were carried out with a snowball sample of HOPE and HS in schools in the Northwest and Southwest of England. Thematic data analysis using NVIVO was used to identify emergent themes.RESULTS:17 core themes were generated, 12 of which confirmed the findings from similar research. However, five themes relating to 'ethos of performance/elitism', 'lower fitness leads to lower ability', 'undervaluing activities within PE dept' or school as a whole', 'role of the school' and 'PE department doing all it can' offer valuable new insight into the factors which may encourage or prevent PA inside or outside the curriculum. CONCLUSION: Despite many positive perceptions of the delivery of PE in schools, it is evident that barriers still exist within that delivery which discourages physical activity. More research is needed to particularly address the complex issues of elitism and the ethos of PA in schools

Testing Fair Wage Theory

Fairness considerations often are invoked to explain wage differences that appear unrelated to worker characteristics or job conditions, but non-experimental tests of fair wage models are rare and weak because of the limits of available market-generated data. In particular, such data rarely permit researchers to (a) identify suitable reference points that employees and employers might use in determining what is fair and (b) control for employees’ marginal output and its value. This study utilizes a unique dataset from the baseball labor market that solves both problems. We find no support for fair wage theory in this market. We also find that fairness premia can be illusory: Wages appear to be adjusted upward for reasons of fairness in regressions that control for variation in individuals’ physical output, but such premia evaporate when the value of that output (which can be market- or firm-specific) is held constant. This suggests that avoiding proxy measures of workers’ marginal revenue products in wage studies might reduce the number of labor market "anomalies" economists must resolve.fairness, efficiency wages, wage differentials

The Existence and Persistence of a Winner’s Curse: New Evidence from the (Baseball) Field

This study takes advantage of recent developments in the measurement and valuation of individual output in the baseball labor market to (i) reassess prior evidence that this market is afflicted by the winner’s curse phenomenon and (ii) test whether bidders learn to avoid this curse over time. Though we find no evidence of negative average returns on player contracts for the earliest cohort of baseball free agents, we conclude that teams in that era failed to efficiently discount their bids in accord with available information, especially about risk. What is more, evidence from a larger sample of players signed in the late 1990s shows that teams have continued to overvalue inconsistent free agents and failed to limit their bids to conform to players’ lower values in small markets. This is consistent with experimental evidence that finds bounded-rational behavior when bidders are faced with complex valuation problems involving multiple elements.market efficiency, bounded rationality, overbidding

Utilising Located Functions to Model and Optimise Distributed Computations

With developments in Grid computing and Web based data storage the task of orchestrating computations is becoming ever more difficult. Identifying which of the available computation resources and datasets to use is not trivial: it requires reasoning about the problem itself and the cost of moving data to complete the computation efficiently. This paper presents a conceptual notation and performance model that enables e-researchers to reason about their computations and make choices about the best use of resources

Bicategories of spans as cartesian bicategories

Bicategories of spans are characterized as cartesian bicategories in which every comonad has an Eilenberg-Moore ob ject and every left adjoint arrow is comonadic

Initial Public Offerings of Ballplayers

As a field study of choice under uncertainty, we examine baseball teams' investments in amateur players. Though most prospects fail to deliver any return on their multi-million dollar signing bonuses, returns on the minority who succeed easily offset these losses: the expected annual yield on the median first-round draftee is 33 percent. However, the pattern of returns is inconsistent with market efficiency. Yields are lower for high schoolers than collegians (27 percent vs. 43 percent), lower for pitchers than position players (24 percent vs. 41 percent), decline for later round long-shots, and may be negative under competitive bidding.Market efficiency; Bounded rationality; Prospect theory; Winner’s curse