Covariance changes detection in multivariate time series

This paper studies the detection of step changes in the variances and in the correlation structure of the components of a vector of time series. Two procedures based on the likelihood ratio test (LRT) statistic and on a cumulative sums (cusum) statistic are considered and compared in a simulation study. We conclude that for a single covariance change the cusum procedure is more powerful in small and medium samples, whereas the likelihood ratio test is more powerful in large samples. However, for several covariance changes the cusum procedure works clearly better. The procedures are illustrated in two real data examples.     

The impact of AIDS on income and human capital

This paper studies the impact of HIV/AIDS on per capita income and education. It explores two channels on how HIV/AIDS affects income that have not been sufficiently stressed by previous literature: the reduction of the incentives to stay in school due to shorter expected longevity and the reduction in productivity of experienced workers. In the model, individuals live for three periods, may get infected in the second period, and with some probability die of AIDS before reaching the third period of their lives. Parents care for the welfare of the future generations so that they will maximize lifetime utility of their dynasty. The simulations predict that the most affected countries in Sub-Saharan Africa in the future will be, on average, 30% poorer than they would be without AIDS. Schooling will decline in some cases by 40%. These figures are dramatically reduced with widespread medical treatment, as it increases the survival probability and productivity of infected individuals.     

Crisis nursery effects on child placement after foster care

The results of a study of the relationship between receiving crisis nursery services and the placement outcomes for young children leaving the child welfare system in Illinois are reported in this paper. The placement outcomes for children leaving foster care whose families received crisis nursery support prior to the children's placement in foster care is compared to the placement outcomes for children whose families received only foster care services. The children in two samples were identified by matching crisis nursery children's data from FY 2006 with children's data in the Illinois Child Abuse and Neglect Tracking System and Children Youth and Services Information System databases. After children served by crisis nursery and foster care services were identified, a comparison group of children with like-characteristics whose families received only foster care services was identified using propensity score matching. The children were followed until their out-of-home placement was terminated or until June 30, 2009. The placement outcomes and the length of stay were compared for the two groups. Using logistical regression analysis the results showed that children whose families received crisis nursery services prior to foster care placement were twice as likely to be reunited with their biological families (birth or extended family members) when compared to children whose families received only foster care services. The difference in the length-of-stay in foster care was not statistically significant when the two groups were compared. This preliminary study using administrative data shows that receiving crisis nursery services may have positive effects on the children's ultimate placement outcome after foster care. Additional research is needed to further explore the relationship between placement outcome and crisis nursery services.     

Alcohol- and drug-involved driving in the United States: methodology for the 2007 National Roadside Survey

This article describes the methodology used in the 2007 U.S. National Roadside Survey to estimate the prevalence of alcohol- and drug-impaired driving and alcohol- and drug-involved driving. This study involved randomly stopping drivers at 300 locations across the 48 continental U.S. states at sites selected through a stratified random sampling procedure. Data were collected during a 2-hr Friday daytime session at 60 locations and during 2-hr nighttime weekend periods at 240 locations. Both self-report and biological measures were taken. Biological measures included breath alcohol measurements from 9,413 respondents, oral fluid samples from 7,719 respondents, and blood samples from 3,276 respondents.     

Representing preorders with injective monotones

Theory and Decision - We introduce a new class of real-valued monotones in preordered spaces, injective monotones. We show that the class of preorders for which they exist lies in between the class...     

ON THE RELATIVE EFFICIENCY OF PERFORMANCE PAY AND NONCONTINGENT INCENTIVES

We report evidence from a large field experiment that compares the effectiveness of contingent and noncontingent incentives in eliciting costly effort for a large range of payment levels. The company with which we worked sent 7,250 letters asking customers to complete a survey. Some letters promised to pay amounts ranging from $1 to $30 upon compliance (contingent incentives), whereas others already contained the money in the request envelopes (noncontingent incentives). Compared to no payment, very small contingent payments lower the response rate while small noncontingent payments raise the response rate. As expected, response rates rise with the size of the incentive offered. The response rate in the noncontingent incentives rises more rapidly for low amounts of incentive, but then flattens out and reaches lower levels than under contingent payments. We discuss how the optimal policy regarding the use of each size and type of incentives crucially depends on firms’ objectives.