Heteroscedastic Global Tests that the Regression Parameters for Two or More Independent Groups are Identical

Simulation results are reported on methods that allow both within group and between group heteroscedasticity when testing the hypothesis that independent groups have identical regression parameters. The methods are based on a combination of extant techniques, but their finite-sample properties have not been studied. Included are results on the impact of removing all leverage points or just bad leverage points. The method used to identify leverage points can be important and can improve control over the Type I error probability. Results are illustrated using data from the Well Elderly II study.     

How Welfare Policies Affect Adolescents' School Outcomes: A Synthesis of Evidence From Experimental Studies

Using data from 8 random assignment studies and employing meta‐analytic techniques, this article provides systematic evidence that welfare and work policies targeted at low‐income parents have small adverse effects on some school outcomes among adolescents ages 12 to 18 years at follow‐up. These adverse effects were observed mostly for school performance outcomes and occurred in programs that required mothers to work or participate in employment‐related activities and those that encouraged mothers to work voluntarily. The most pronounced negative effects on school outcomes occurred for the group of adolescents who had a younger sibling, possibly because of the increased home and sibling care responsibilities they assumed as their mothers increased their employment.     

The Market Provision of Management Services, Information Asymmetries and Service Quality—Some Market Solutions: an Empirical Example

This article examines the problems of information asymmetry associated with the market provision of managerial services. Such problems are heightened by those characteristics which differentiate services from goods. Two unique, and central, characteristics of services, are intangibility and perishability. These create special problems for the market provision of services. In particular they make for difficulties in assessing quality; whereas the producer may know product quality, the buyer often does not. The asymmetry between sellers and buyers is of two types: Adverse selection and moral hazard. Adverse selection occurs when the buyer cannot observe the relevant characteristics of the seller or the conditions under which they work. The problem of moral hazard is the buyer's inability to observe the action taken by the sellers. If these difficulties are not overcome, the market could collapse as companies withdraw and internalize service provision. However, each market has a number of in-built mechanisms which remedy the harmful effects associated with information-related problems. The institutional arrangements which predominate in particular markets are dependent upon the trust-producing mechanisms within those markets. Consequently, market responses to information asymmetries are far from uniform. The argument is illustrated using the example of the executive recruitment industry. In this respect the paper is a highly focused study of those mechanisms which overcome information asymmetries in one service market.     

Rainfall interception by Santa Monica's municipal urban forest

Effects of urban forests on rainfall interception and runoff reduction have been conceptualized, but not well quantified. In this study rainfall interception by street and park trees in Santa Monica, California is simulated. A mass and energy balance rainfall interception model is used to simulate rainfall interception processes (e.g., gross precipitation, free throughfall, canopy drip, stemflow, and evaporation). Annual rainfall interception by the 29,299 street and park trees was 193,168 m³ (6.6 m³/tree), or 1.6% of total precipitation. The annual value of avoided stormwater treatment and flood control costs associated with reduced runoff was $110,890 ($3.60/tree). Interception rate varied with tree species and sizes. Rainfall interception ranged from 15.3% (0.8 m³/tree) for a small Jacaranda mimosifolia (3.5 cm diameter at breast height) to 66.5% (20.8 m³/tree) for a mature Tristania conferta (38.1 cm). In a 25-year storm, interception by all street and park trees was 12,139.5 m³ (0.4%), each tree yielding $0.60 (0.4 m³/tree) in avoided flood control costs. Rainfall interception varied seasonally, averaging 14.8% during a 21.7 mm winter storm and 79.5% during a 20.3 mm summer storm for a large, deciduous Platanus acerifolia tree. Effects of differences in temporal precipitation patterns, tree population traits, and pruning practices on interception in Santa Monica, Modesto, and Sacramento, California are described.