A study of expert overconfidence

Overconfidence is one of the most common (and potentially severe) problems in expert judgment. To assess the extent of expert overconfidence, we analyzed a large data set on expert opinion compiled by Cooke and colleagues at the Technical University of Delft and elsewhere. This data set contains roughly five thousand 90% confidence intervals of uncertain quantities for which the true values are now known. Our analysis assesses the overall extent of overconfidence in the data set. Significant differences in the extent of overconfidence were found among studies, among experts, and among questions within a study. Moreover, replications (multiple realizations for the same question) allowed a preliminary assessment of whether the question effect is due largely to question difficulty, or merely to random noise in the realizations of the uncertain quantities. The results of this analysis suggest that much of the apparent question effect may be due to noise rather than systematic differences in the difficulty of achieving good calibration for different questions. The results support the differential weighting of experts, since there are significant differences in expert calibration within studies.     

Validity conditions in repeated measures designs.

This article has 2 objectives. The 1st is to present necessary and sufficient conditions for the validity of traditional within-S F tests in repeated measures designs. It is shown that the Mauchly sphericity criterion (W) and possibly the Box test for the equality of covariance matrices are appropriate to judge the validity of these conditions. Valid applications of both tests are conducted on sets of orthogonal normalized variables that are associated with each cluster of within-S mean square ratios. The 2nd objective of the article is to present empirical results on the appropriateness of using the W criterion when the variates are not normally distributed. For light-tailed distributions the W criterion was shown to be moderately conservative, whereas for heavy-tailed distributions, empirical Type I error rates exceeded nominal alpha. Since most social science applications typically involve light-tailed rather than heavy-tailed distributions, the W criterion should provide useful results in most cases. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The influence of compositional and microstructural variations on the mechanism of static fracture in aluminum alloys

The object of the paper is to examine the effects of alloy purity and state of aging on the fracture mechanism and resultant toughness of pure Al-Cu alloys, and commercial duralumin. In pure alloys, the transition from a shear to an intergranular mode of fracture with overaging is associated with changes in the nature and size of the matrix precipitate, which affect the slip character. In the corresponding commercial purity alloys, no such fracture mode transition occurs. The presence of second-phase dispersoids inhibits planar slip, and in the overaged state inclusion-matrix interfaces present a suitable alternative site to the grain boundaries for strain accumulation, resulting in debonding leading to the initiation of voids, which subsequently grow and coalesce. The fracture toughness, as conventionally measured, indicates the material’s resistance to crack initiation rather than propagation and is effectively independent of fracture mode. The work hardening capacity has a marked effect on void size, and is shown to be a sensitive indicator of fracture toughness in both pure and commercial alloys. Based on a simple model, good agreement is obtained between experimental results of toughness and those predicted from a knowledge of the tensile properties.     

Fibre-matrix interface effects in asbestos-cement composites

The microstructure and failure mode of the fibre—matrix interfacial region in asbestoscement composites have been investigated, primarily by scanning electron microscopy. Processes of bonding and debonding are shown to be complex, involving a variety of mechanismS. Mutual interlocking has been observed between asbestos fibrils and calcium silicate hydrate needles, whereas fibre pull-out occurs primarily through matrix failure adjacent to the interface, together with some interfibre separation.     

A micro-model of internal supply forecasting for technical manpower planning

The manpower planning process includes forecasting the future demand for manpower and the future internal supply of manpower and then developing action plans which will balance supply and demand. Many of the models which exist for forecasting internal supply are for periods of one year or longer, which makes them inappropriate for many project planning and short term human resource management applications. This paper presents an easily implemented short-range (12-month horizon) model for forecasting internal supply. Time series analysis techniques are used to identify seasonal patterns and trends which exist in the determinants of internal supply. These are employed in the development of an internal supply forecast at both the aggregate firm level and at the individual skill group level. Feasibility of the model is demonstrated using empirical data. Output of the model is useful for further manpower planning.     

Family structure, psychological separation, and college adjustment: A canonical analysis and cross-validation.

554 undergraduates from intact families completed relevant instruments. A canonical correlation of family-structure and psychological-separation scores extracted 2 significant and stable roots, representing conflictually overinvolved and differentiated family patterns, respectively. Intercorrelations of each variate with original variables indicate that these dimensions were also associated with different separation patterns across subject sex. The canonical correlation of psychological-separation and college-adjustment measures uncovered a single significant and stable root that underscored the relation of conflictual independence and personal adjustment within both male and female groups. The results are interpreted as supporting assumptions of structural family theory and as suggesting that the psychological separation patterns of college men and women are differentially affected by inappropriate family structure. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Constrained cracking in glass fibre-reinforced epoxy cross-ply laminates

Specimens of 90° cross-ply glass-reinforced epoxy resins were tested in tension parallel to the direction of reinforcement in the outer plies. The thickness of the inner ply was varied and cracking constraint was observed at small thicknesses. At large inner-ply thicknesses the specimens showed uniform transverse cracking, and at very low inner-ply thicknesses this transverse cracking could be suppressed completely prior to total specimen failure. Fracture toughness values were determined on transverse unidirectional laminates of the same volume fraction. It was found that the cracking constraint observed can be accounted for, using the theory of Aveston and Kelly.     

Analytical ultracentrifugation for characterizing nanocrystals and their bioconjugates

Analytical ultracentrifugation (AU) provides a general way to probe the polydispersity of nanoparticles and the formation of bioconjugates in solution. Unconjugated gold nanocrystals show sedimentation coefficient distributions that are in agreement with size distributions as measured by TEM. AU is sensitive to the size/shape changes elicited by conjugation, in this case to lactose repressor (LacI). AU data reveal saturating protein concentrations for conjugates that correspond to the measured stoichiometry of the complex under these conditions.