Bipolar items for the measurement of personal optimism instead of unipolar items

A personal optimism scale composed of unipolar items is transformed into a scale composed of bipolar items. The transformation is performed because of the item wording problem that denotes the lack of homogeneity in scales composed of positively and negatively worded items. The original optimism scale for the assessment of personal optimism comprises eight unipolar items. It is transformed into a scale with four bipolar items by merging pairs of items. In confirmatory factor analysis the scale based on bipolar items showed an acceptable degree of good model fit. Furthermore, the personal optimism latent variables of the two types of items showed to be equivalent when investigating trait-specific equivalence.