Inverse Probability Weighting with Missing Predictors of Treatment Assignment or Missingness

Inverse probability weighting (IPW) can deal with confounding in non randomized studies. The inverse weights are probabilities of treatment assignment (propensity scores), estimated by regressing assignment on predictors. Problems arise if predictors can be missing. Solutions previously proposed include assuming assignment depends only on observed predictors and multiple imputation (MI) of missing predictors. For the MI approach, it was recommended that missingness indicators be used with the other predictors. We determine when the two MI approaches, (with/without missingness indicators) yield consistent estimators and compare their efficiencies.We find that, although including indicators can reduce bias when predictors are missing not at random, it can induce bias when they are missing at random. We propose a consistent variance estimator and investigate performance of the simpler Rubin’s Rules variance estimator. In simulations we find both estimators perform well. IPW is also used to correct bias when an analysis model is fitted to incomplete data by restricting to complete cases. Here, weights are inverse probabilities of being a complete case. We explain how the same MI methods can be used in this situation to deal with missing predictors in the weight model, and illustrate this approach using data from the National Child Development Survey.     

The Use of PBPK Models to Inform Human Health Risk Assessment: Case Study on Perchlorate and Radioiodide Human Lifestage Models

Physiologically‐based pharmacokinetic (PBPK) models are often submitted to or selected by agencies, such as the U.S. Environmental Protection Agency (U.S. EPA) and Agency for Toxic Substances and Disease Registry, for consideration for application in human health risk assessment (HHRA). Recently, U.S. EPA evaluated the human PBPK models for perchlorate and radioiodide for their ability to estimate the relative sensitivity of perchlorate inhibition on thyroidal radioiodide uptake for various population groups and lifestages. The most well‐defined mode of action of the environmental contaminant, perchlorate, is competitive inhibition of thyroidal iodide uptake by the sodium‐iodide symporter (NIS). In this analysis, a six‐step framework for PBPK model evaluation was followed, and with a few modifications, the models were determined to be suitable for use in HHRA to evaluate relative sensitivity among human lifestages. Relative sensitivity to perchlorate was determined by comparing the PBPK model predicted percent inhibition of thyroidal radioactive iodide uptake (RAIU) by perchlorate for different lifestages. A limited sensitivity analysis indicated that model parameters describing urinary excretion of perchlorate and iodide were particularly important in prediction of RAIU inhibition; therefore, a range of biologically plausible values available in the peer‐reviewed literature was evaluated. Using the updated PBPK models, the greatest sensitivity to RAIU inhibition was predicted to be the near‐term fetus (gestation week 40) compared to the average adult and other lifestages; however, when exposure factors were taken into account, newborns were found to be populations that need further evaluation and consideration in a risk assessment for perchlorate.     

Reclaiming Futures initiative from a Sicangu Lakota tribal perspective: Lessons shared

This paper tells a story about one of the initiatives sponsored by the Robert Wood Johnson Foundation known as Oyate Teca Owicakiya (Helping Young People). Oyate Teca Owicakiya was located on the Rosebud reservation, an extremely rural area in South Dakota. This was the only indigenous-based initiative funded by the Foundation. The initiative was undertaken by the Sinte Gleska University to provide services to reclaim youth from the justice system. This collaborative built on existing structures and community networks to strengthen and coordinate services for youth. The Reclaiming Futures model was adapted to the local setting by utilizing tribal resources. The background of the setting, its unique tribal governmental structure, demographics, and socioeconomic indicators are presented, and finally, eleven lessons are discussed. The success of the initiative was the strength and resiliency of the community itself, its members, and the network of individuals and organizations who came together for troubled tribal youth and their families.     

Exposure to international migration and its effect on childbearing in Turkey

International migration alters social norms, family structures, and population development in sending regions. Each of these factors affects fertility, making the impact of international migration on childbearing an increasingly important area of study. In many sending regions, the Demographic and Health Surveys (DHS) provide a promising, but underutilized, source of data for understanding the relationship between international migration and childbearing. Using the household and individual questionnaires in the 2003 Turkish DHS, we develop a multi-layered approach for measuring international migration. We then use these measures to examine differences in childbearing among women in migrant and non-migrant households, assessing the effects of migrant selection and migration-related roles and attitudes on the number of children born. After adjusting for selection characteristics, we find return female migrants and migrant wives are not significantly different from women in non-migrant households; role and attitude differences have only modest impacts on the association between women’s exposure to migration and childbearing.     

Social skills of adopted Chinese girls at home and in school: Parent and teacher ratings

This study examines adopted Chinese girls' social skills at home and in school as well as the effect of pre-adoption adversity on these skills. Parent ratings of 869 girls and teacher ratings of 611 of the 869 girls were obtained using the Social Skills Rating System for parent (SSRS-P) and teacher (SSRS-T) respectively. The girls were adopted on average at 15.6 months (SD = 13.9) and were in three age groups, including preschool, elementary school, and secondary school. Data on five indicators of pre-adoption adversity (i.e., signs/symptoms, delays at adoption, initial refusal/avoidance of adoptive mothers, crying/clinging behaviors, and age at adoption) were obtained from the same adoptive parents 2 years prior. Findings suggest that both parents and teachers rated the girls as either similar to or better than US norms on the SSRS. Parent–teacher agreement on SSRS subscales was significant but modest (rs = 0.12–0.25). Two indicators of pre-adoption adversity (i.e., delays at adoption and initial refusal/avoidance of adoptive mothers) predicted poorer social skills at home; two other indicators of pre-adoption adversity (i.e., signs/symptoms and age at adoption) predicted poorer social skills in school.     

How Inventory Cost Influences Introduction Timing of Product Line Extensions

In the industry with radical technology push or rapidly changing customer preference, it is firms' common wisdom to introduce high‐end product first, and follow by low‐end product‐line extensions. A key decision in this “down‐market stretch” strategy is the introduction time. High inventory cost is pervasive in such industries, but its impact has long been ignored during the presale planning stage. This study takes a first step toward filling this gap. We propose an integrated inventory (supply) and diffusion (demand) framework and analyze how inventory cost influences the introduction timing of product‐line extensions, considering substitution effect among successive generations. We show that under low inventory cost or frequent replenishment ordering policy, the optimal introduction time indeed follows the well‐known “now or never” rule. However, sequential introduction becomes optimal as the inventory holding gets more substantial or the product life cycle gets shorter. The optimal introduction timing can increase or decrease with the inventory cost depending on the marketplace setting, requiring a careful analysis.     

An assessment of occupational and organizational commitment: A multivariate analysis

Data from 120 park and forest rangers were used to empirically assess the relative impact of sociodemographic, attitudinal, and organizational factors on both occupational and organizational commitment. Through the use of multiple regression analysis, sociodemographic and attitudinal factors were shown generally to bear a positive relationship to both types of commitment. Upon further analysis of partials based on type of occupation, some specification of the original relationships was noted, thereby indicating a note of caution in generalizing findings concerning occupational and organizational commitment from one group of occupational practitioners to another.