A mantra often repeated in the introductory material to psychometrics and Item Response Theory (IRT) is that a Rasch model probabilistic version of Guttman scale. The idea comes from observation sigmoidal item response function provides characteristic models an It appears, however, more difficult reconcile assumption local independence, which traditionally accompanies model, with dependence exi...

Two conservative approaches are proposed to a semidefinite programming problem nonlinearly dependent on uncertain parameters. These approaches are applicable to general nonlinear parameter dependence not necessarily polynomial or rational. They are based on a mild assumption that the parameter dependence is expressed as the difference of two convex functions. The first approach uses constant bo...

this study took an epidemiological approach toward the problem of drug addiction in tehran. the subjects were 300 addicts chosen on the basis of stratified random selection out of the population of 3627 prisoners who were all proven addicts and sentenced to imprisonment by the court in the year 1370. a descriptive survey showed that drug addiction generally, and heroin addiction specifically, i...