Mites and Wee Beasties

Abstract

The subtitle of this paper could be “Humans versus Arthropods.” Of the several classes of arthropods, Arachnida and Insecta are the most important from the public health standpoint. Arthropods are among man's most formidable competitors and they can affect the health of humans by being vectors of pathogenic microorganisms, by invading tissues, by inoculating poisonous substances, and by being pests.

A review is made of public health aspects of some arthropods that might be seen on a university or college campus. The diseases and infestations caused by mites (scabies), lice (pediculosis), bed bugs, fleas, and ticks are discussed.     

Power-Law Adjusted Survival Models

A simple adjustment to parametric failure-time distributions, which allows for much greater flexibility in the shape of the hazard-rate function, is considered. Analytical expressions for the distributions of the power-law adjusted Weibull, gamma, log-gamma, generalized gamma, lognormal, and Pareto distributions are given. Most of these allow for bathtub-shaped and other multi-modal forms of the hazard rate. The new distributions are fitted to real failure-time data which exhibit a multi-modal hazard-rate function and the fits are compared.     

Robustness estimators of location:a classification of linear and adaptive estimators

Real-world data sets may be described in terms similar to trauma cases- 'messy' with 'high morbidity'. Alternative estimators to the traditional mean are examined via a simulation study over a wide range of both symmetric and asymmetric distributions. These alternative estimators are data depenmdent and, in most cases, represent data far better than the usual mean. Princeton and post-Princeton linear and adaptive estimators of location are summarized, and a classification scheme based on an ancillary or selector statistic is proposed. The computational formulae for the collection of estimators have been standardized, as have the ancillary statistics. We classify these estimators by their computational form, give the computational formulae for each in a standardized notation, evaluate the subclass of estimators, and identify our 'winner' in that class.     

Robust Two-Sample Statistics for Testing Equality of Means: a Simulation Study

When testing the equality of the means from two independent normally distributed populations given that the variances of the two populations are unknown but assumed equal, the classical two-sample t-test is recommended. If the underlying population distributions are normal with unequal and unknown variances, either Welch's t-statistic or Satterthwaite's Approximate F-test is suggested. However, Welch's procedure is non-robust under most non-normal distributions. There is a variable tolerance level around the strict assumptions of data independence, homogeneity of variances and normality of the distributions. Few textbooks offer alternatives when one or more of the underlying assumptions are not defensible.     

Relationships between physical activity and the proximity of exercise facilities and home exercise equipment used by undergraduate university students

The authors used stratified random sampling procedures to investigate the relationships among physical activity (PA), the proximity of exercise facilities, and the quantity of home exercise equipment in a sample of 411 undergraduates. To examine the data they collected from the modified Godin Leisure-Time Exercise Questionnaire and the Home Environment Questionnaire, the authors used correlational analyses and analysis of variance. Intensity and duration of PA showed a significant relationship to the proximity of exercise facilities. Intensity, frequency, and duration of PA were significantly related to the quantity of students' home exercise equipment. Freshmen and sophomores engaged in PA closer to their residences and participated in 3 more exercise bouts per week than juniors and seniors. These findings suggest that proximity of the activity episode may have an effect on PA behavior of college students.     

A methodological approach to strategic petroleum reserves

Energy constitutes a small fraction of the production inputs in the economy, yet the rigidity imposed by the short and medium term inability to substitute energy with other production factors in case of an energy shortage, requires the establishment of safeguard mechanisms to ensure sufficient energy supply during an emergency. These safeguards usually take the form of strategic energy reserves. A methodological approach is presented here, relating the level of strategic petroleum reserves, the decision variable, with the costs associated with their storage and the economic losses incurred by an energy shortage. This approach is based on the use of a decision tree, to portray emergency scenarios. Each scenario, a branch of the decision tree, can be evaluated in terms of a cost function which includes the inventory procurement and maintenance cost and the shortage cost inflicted by a petroleum shortfall.