Testing hypotheses when there could be an initial effect

In many treatment-versus-control experiments, the observed random variables can be written as the product of a Bernoulli and a continuous random variable. The treatment can affect the distribution of the observations in two ways.

1. the probability that the observation is 0 could be altered.

2. the distribution of the nonzero observations could be changed.

We may also want to measure the combined effect of the treatment.

3. the expected value of control and treated units may differ.

A method is presented for testing for the presence of the combined effect when the general form of the distribution function of the continuous observations is known. For the case when this distribution function is from the family of gamma distributions, a previously proposed test criterion for the combined effect has poor power properties. In this paper, we discuss a test criterion that has improved power properties.     

Confidence intervals for the interrater agreement measure kappa

The asympotic normal approximation to the distribution of the estimated measure [kcirc] for evaluating agreement between two raters has been shown to perform poorly for small sample sizes when the true kappa is nonzero. This paper examines the use of skewness corrections and transformations of [kcirc] on the attained confidence levels. Small sample simulations demonstrate the improvement in the agreement between the desired and actual levels of confidence intervals and hypothesis tests that incorporate these corrections.     

Sex Differences in Biomechanics Associated with Knee Osteoarthritis

Osteoarthritis of the knee is seen more frequently in females than males. However, few studies have examined the interplay of gender, gait mechanics, pain, and disability in persons with osteoarthritis. This study examines the influence of anthropometrics, radiographic disease severity, pain, and disability on gender differences in gait mechanics in patients with knee osteoarthritis. Gait mechanics for 26 men and 30 women were collected using 3-D kinematics and kinetics. Women had a significantly lower knee adduction moment than men and a significantly higher stride frequency. Within female subjects, variations in gait mechanics were primarily explained by weight, BMI, pain, and disability. In males, variations in gait mechanics were primarily explained by age and disability.     

Reducing Absenteeism and Rescheduling Among Grocery Store Employees With Point-Contingent Rewards

The purpose of this research was to evaluate a reward program designed to reduce absenteeism among staff (N = 38) at a grocery store. The intervention included public feedback and a credit reward system whereby participants got store dollars for attendance and authorized rescheduling of work assignments. Results showed that absenteeism decreased from a group mean of 8 shifts missed per week during baseline to 4.25 shifts missed per week during the intervention before increasing to 6.75 shifts missed per week during the reversal phase. The mean total rescheduling occurrences were reduced from a baseline average of 19.83 per week to 9.25 per week during the intervention and returned to 22.25 per week during the reversal. Employees were also less likely to leave early during the intervention period.     

Analysis of fertility using cohort-specific socio-economic data

Review of Economics of the Household - In this paper we propose a novel approach that relates age-specific cohort fertility rates with socioeconomic conditions faced by each cohort in each single...