Issues in the interpretation of the results of school effectiveness research

In this chapter three issues in the interpretation of the results of school effectiveness research are discussed: criterion choice, effect size and stability of effects. With respect to the first issue the overall conclusion is, that criterion choice and definition depend on the effectiveness perspective and the particular theory one wishes to corroborate. The issues of effect size and stability of school effects are treated both from the angle of a synthesis of available empirical results and from the angle of conceptual analysis. An overall evaluation of the available data on effect size and stability leads to the conclusion that school effectiveness models are not as shaky as certain critics would have it, but at the same time not established as firmly as enthusiastic school improvers treat them. Various suggestions as to the improvement of future school effectiveness research are offered, notably more refined research designs and more elaborate theory development

A Lindley-type equation arising from a carousel problem

In this paper we consider a system with two carousels operated by one picker. The items to be picked are randomly located on the carousels and the pick times follow a phase-type distribution. The picker alternates between the two carousels, picking one item at a time. Important performance characteristics are the waiting time of the picker and the throughput of the two carousels. The waiting time of the picker satisfies an equation very similar to Lindley's equation for the waiting time in the PH/U/1 queue. Although the latter equation has no simple solution, we show that the one for the waiting time of the picker can be solved explicitly. Furthermore, it is well known that the mean waiting time in the PH/U/1 queue depends on to the complete interarrival time distribution, but numerical results show that, for the carousel system, the mean waiting time and throughput are rather insensitive to the pick-time distribution.Comment: 10 pages, 1 figure, 19 reference

Social experiments and intrumental variables with duration outcomes

This paper examines the empirical analysis of treatment effects on duration outcomes from data that contain instrumental variation. We focus on social experiments in which an intention to treat is randomized and compliance may be imperfect. We distinguish between cases where the treatment starts at the moment of randomization and cases where it starts at a later point in time. We derive exclusion restrictions under various informational and behavioral assumptions and we analyze identifiability under these restrictions. It turns out that randomization (and by implication, instrumental variation) by itself is often insufficient for inference on interesting effects, and needs to be augmented by a semi-parametric structure. We develop corresponding non- and semi-parametric tests and estimation methods.Event-history analysis; intention to treat; non-compliance; policy evaluation; selection

Dynamically assigned treatments: duration models, binary treatment models, and panel data models

Often, the moment of a treatment and the moment at which the outcome of interest occurs are realizations of stochastic processes with dependent unobserved determinants. Notably, both treatment and outcome are characterized by the moment they occur. We compare different methods of inference of the treatment effect, and we argue that the timing of the treatment relative to the outcome conveys useful information on the treatment effect, which is discarded in binary treatment frameworksProgram evaluation; treatment effects; bivariate duration analysis; selection bias; hazard rate; unobserved heterogeneity; fixed effects; random effects

Physico-Chemical Studies on Dusts of Small Particle Size

A brief description is given of the respiratory system and the way in which it deals with inhaled dusts; of the methods employed for sampling and analysing airborne dusts; of the methods employed in mines to suppress the fine dust particles; and of the mechanism of atomisation of aqueous media applied in dust suppression. An apparatus has been developed for the examination of the settling characteristics of fine dust clouds. This consists of a chamber fitted with a pair of photoelectric cells and connected to a recording instrument for the continuous measurement of the dust concentration. Dust present in the chamber intercepts some of the light reaching one of the cells and produces a differential current which is measured by the recorder. A thermal precipitator is incorporated in the apparatus for the calibration of the photoelectric cell system and also to enable samples of the dust clouds to be withdrawn for microscopic examination. Sedimentation studies have been carried out using various dusts. The results show that the dusts sediment rapidly over the first few hours, after which the rate of disappearance is less rapid until only the very small particles remain, when sedimentation is very slow. A compressed-air spray has been developed and calibrated, and the effects of alterations to the variables studied. The results indicate that the nozzle dimensions have no effect on atomisation, hut atomisation increases as the air rate and the velocity differential between air and water are increased. Atomisation decreases slightly as the sampling distance from the nozzle is increased. The effects of the air blast used for atomisation on the sedimenting dust cloud, have been studied and two theories have been put forward to account for them. The results show that more dust is removed than is predicted by theory. The effect of the water spray on the sedimenting dust cloud has been studied. The results indicate that a proportion of the dust cloud is removed. The amount of dust removed is increased as the atomisation, droplet velocity and duration of spraying are increased. The effect of the compressed-air spray on the size distribution of the dust in the suspended cloud has been investigated. The results show that the air blasts have little effect on the size distribution of the dust cloud, but the water sprays remove a proportion of all sizes of particles. A greater percentage of the >0.83mu particles is removed as the droplet diameter is decreased. The percentage of 0.83mu particles removed is increased whereas the percentage of <0.83mu particles removed is decreased. An instrument has been designed and made (the H-J sampler) which enables fairly large samples of airborne mine dusts to be collected from the atmosphere of the pit. Trials carried out underground have given good results. A comparison has been made with another manufactured sampler (the Hexhlet, designed by Wright) and it has been found that the H-J sampler gives larger samples and that this outweighs the advantage of the elutriater on the Hexhlet