Development of a “Perceived Stress Scale" Based on Classical Test Theory and Graded Response Model

Abstract

Themain purpose of this study is to develop a perceived stress scale based onClassical Test Theory (CTT) and Graded Response Model (GRM); to compare theparameters of the items in the scale that are tried to be developed accordingto both models, and to determine under which theory the measurement toolproduces more reliable and valid results according to these compared itemparameters. The item discrimination parameter value calculated according to CTTranges from 0.472 to 0.735. On the other hand, item discrimination parametervalues calculated under GRM vary between 1.062 (Item 15) and 2.606 (Item 2).Correlations between item thresholds were tested and the calculated correlationcoefficients were; r =0.840 for β1 (p<0.01), r = 0.947 for β2 (p<0.01), r= 0.713 for β3 (p<0.05), and r = 0.559 for β4 (p<0.05) respectively. Itcan be assumed that these values not only support the item invariance of theitems in the scale, but also show that the GRM is suitable for the data usedfor the scaling of the items. The reliability coefficient of the scale, interms of internal consistency, was calculated as 0.919 according to the CTT,while the marginal reliability coefficient calculated as 0.931 according toGRM. Both reliability coefficients are quite high. In conclusion, there is ahigh correlation between the item parameters calculated according to bothapproaches, and the perceived stress scale (PSS) that is being developed canmeasure the desired features.

Keywords

• classical test theory
• item response theory
• item difficulty
• item discrimination index
• item invariance
• classical test theory
• item response theory
• item difficulty
• item discrimination index