An Empirical Approach to Sufficient Similarity: Combining Exposure Data and Mixtures Toxicology Data

When assessing risks posed by environmental chemical mixtures, whole mixture approaches are preferred to component approaches. When toxicological data on whole mixtures as they occur in the environment are not available, Environmental Protection Agency guidance states that toxicity data from a mixture considered “sufficiently similar” to the environmental mixture can serve as a surrogate. We propose a novel method to examine whether mixtures are sufficiently similar, when exposure data and mixture toxicity study data from at least one representative mixture are available. We define sufficient similarity using equivalence testing methodology comparing the distance between benchmark dose estimates for mixtures in both data‐rich and data‐poor cases. We construct a “similar mixtures risk indicator”(SMRI) (analogous to the hazard index) on sufficiently similar mixtures linking exposure data with mixtures toxicology data. The methods are illustrated using pyrethroid mixtures occurrence data collected in child care centers (CCC) and dose‐response data examining acute neurobehavioral effects of pyrethroid mixtures in rats. Our method shows that the mixtures from 90% of the CCCs were sufficiently similar to the dose‐response study mixture. Using exposure estimates for a hypothetical child, the 95th percentile of the (weighted) SMRI for these sufficiently similar mixtures was 0.20 (i.e., where SMRI <1, less concern; >1, more concern).     

Evaluation of the parameters of su by rational fractions

A rational fraction approximation is given for a function of one of the parameters defining Johnson's S_UError assessment for a segment of the domain of validity shows remarkable accuracy.     

On the one-sample location hypothesis for mixed bivariate data

We study a hypothesis testing problem involving the location model suggested by Olkin and Tate (1961). Specifically, we derive a likelihood ratio lest of the associated location hypothesis as an alternative to the conventional method of carrying out separate tests for each of the parameters. A small sample Monte Carlo comparison indicates the general superiority of the former in terms of statistical power. We also comment briefly on the properties of the test.     

Connections and Constraints: The Effects of Children on Caregiving

This article assesses the effects of children on parents' involvement in caregiving. On the basis of interviews with 273 respondents, we address the effects of having children on care given to kin and nonkin; assess the effects of children's characteristics, especially age and gender, on the help mothers and fathers provide; and examine how these vary with mothers' employment. Overall, we find that the presence of children connects parents into networks of care more than it constrains them. The effects vary depending on the characteristics of the child (including age and gender) as well as characteristics of the parent (like gender and employment).     

Can Demographic Variables Predict Lottery and Pari-mutuel Losses? An Empirical Investigation

Using data from the 2004 and 2005 Consumer Expenditure Surveys (CES) comprising of 15,000 respondents, this study examines two research questions. The first of these considers the demographic differences between households whose members lose money playing the lottery and/or engaging in pari-mutuel betting and those whose members do not lose money participating in such activities. The second assesses demographic differences among households whose members lose money playing the lottery and/or engaging in pari-mutuel betting. It was found that respondents living in money-losing households are slightly older, better off financially, more likely to be married or divorced, more likely to live in a state with at least one legal casino and more likely to live in the Northeast than respondents living in non-money-losing households. Among those living in money-losing households, the least wealthy and African American respondents are more likely to lose a higher proportion of their respective incomes purchasing lottery tickets and engaging in pari-mutuel betting than wealthier respondents and whites.     

Confounding in mixed factorial experiments through isomorphisms

The derivation of a simpie mexhoa for confounding in mixed factorial experiments from an isomorphism of finite abelian groups is presented. The theoretical bases of confounding procedures that use modular arithmetic for such experiments are compared.     

Exact confidence bounds for an exponential parameter under hybrid censoring

Consider a life testing experiment in which n units are put on test, successive failure times are recorded, and the observation is terminated either at a specified number r of failures or a specified time T whichever is reached first. This mixture of type I and type II censoring schemes, called hybrid censoring, is of wide use. Under this censoring scheme and the assumption of an exponential life distribution, the distribution of the maximum likelihood estimator of the mean life 6 is derived. It is then used to construct an exact lower confidence bound for θ.