The use of extreme groups in assessing relationships

The relationship between variables in applied and experimental research is often investigated by the use of extreme (i.e., upper and lower) groups. Earlier analytical work has demonstrated that the extreme groups procedure is more powerful than the standard correlational approach for some values of the correlation and extreme group size. The present article provides methods for using the covariance information that is usually discarded in the classical extreme groups approach. Essentially, then, the new procedure combines the extreme groups approach and the correlational approach. Consequently, it includes the advantages of each and is shown to be more powerful than either approach used alone.     

The influence of communality,factor strength,and loading size on the sampling characteristics of factor loadings

A Monte Carlo approach is employed in determining whether or not certain variables produce systematic effects on the sampling variability of individual factor loadings. A number of sample correlation matrices were generated from a specified population, factored, and transformed to a least-squares fit to the population values. Influences of factor strength, communality and loading size are discussed in relation to the statistics summarizing the results of the above procedures. Influences producing biased estimators of the population values are also discussed.This study was supported in part by NSF Grant GB 4230. Computing assistance was obtained from the Western Data Processing Center and Health Sciences Computing Facility, UCLA, sponsored by NIH Grant FR-3.     

Making Sense of Moral Realism

The article begins by surveying defences of moral realism and noting the revival of an ontology of 'moral properties'. Such a position tends either to invite accusations of espousing metaphysically 'queer' properties, or to fall back on a weak (e.g. externalist) version of moral realism. Norman attempts to find a way through these difficulties by exploring the idea of 'moral vision', suggesting that this is best understood not as the intuiting of special moral properties but as a matter of 'seeing patterns' in our lives and experiences. Such an account of moral vision can explain how it can be both cognitive and action-guiding.     

Combat Exposure and Posttraumatic Stress Disorder Among Portuguese Special Operation Forces Deployed in Afghanistan

Several combat- and noncombat-related stressors have been reported in Afghanistan. There is now accumulating evidence that suggests that posttraumatic stress disorder (PTSD) is linked to combat experiences; however, little is known about how these exposures might affect elite combat troops. This research aims to evaluate the prevalence of combat and noncombat related stressors, as well as PTSD in Portuguese Special Forces deployed in Afghanistan. Overall, participants reported high levels of exposure to combat and adverse physical conditions but also high levels of within-unit comradeship. The analysis also exposed that 2.7% of the participants reported symptoms compatible with PTSD and 8.8% with compatible partial PTSD. When the authors conducted a binary logistic regression, only the higher levels of combat exposure explained the symptoms of PTSD.     

Ordinal test fidelity estimated by an item sampling model

A test theory using only ordinal assumptions is presented. It is based on the idea that the test items are a sample from a universe of items. The sum across items of the ordinal relations for a pair of persons on the universe items is analogous to a true score. Using concepts from ordinal multiple regression, it is possible to estimate the tau correlations of test items with the universe order from the taus among the test items. These in turn permit the estimation of the tau of total score with the universe. It is also possible to estimate the odds that the direction of a given observed score difference is the same as that of the true score difference. The estimates of the correlations between items and universe and between total score and universe are found to agree well with the actual values in both real and artificial data.Part of this paper was presented at the June, 1989, Meeting of the Psychometric Society. The authors wish to thank several reviewers for their suggestions. This research was mainly done while the second author was a University Fellow at the University of Southern California.