Measuring Dispositional Optimism: Item Response Theory (IRT) Analyses of the Life Orientation Test – Revised

The Life Orientation Test – Revised (LOT-R) is the most used instrument to assess dispositional optimism, a personality characteristic influencing psychological functioning, subjective well-being and physical health. Aim of our research is to analyze the properties of the LOT-R by performing Item Response Theory (IRT) analysis and assess its construct and criterion validity. In the first study the LOT-R was administered to a sample of 2,862 Italian adults. Items’ properties and the equivalence of the items across age and gender were evaluated by applying IRT analyses and Differential Item Functioning (DIF). Results demonstrated that the LOT-R is able to distinguish people with different levels of optimism and cover the entire latent trait continuum. The items are gender and age invariant.Participants in a second study were 774 Brazilian and 809 Italian adults. Results of the IRT analysis confirmed the good properties of the LOT-R in the Italian sample. In the Brazilian sample, the scale appears less effective for the high optimism levels. Results of the DIF test between the two samples demonstrated the non-equivalence of the difficulty parameter for all the items. Moreover, in both study, by evaluating concurrent relationships with psychological and subjective well-being, the LOT-R showed good construct and criterion validity. To sum up, the LOT-R is a valid measure of optimism and it is suitable in the various field of empiricaland practical psychology.