The current research is aimed at scaling Psychasthenia scale of Minnesota Multiphasic Personality Inventory 2 , access to a new form and brief to the test, it,s liberal from the sample and items properties, using one and pair parameter models, and testing the effect of two variables in the results of scaling Psychasthenia scale (the model used, the sample size) with using criteria of accuracy as the Standard Error, Relaibility and Information Function.