Developing, evaluating, and interpreting personality state measures: A framework based on the revised latent state-trait theory

States are increasingly important in personality theory and research. Yet, the assessment of personality states usually relies on ad hoc measures whose development and evaluation are largely separated from theoretical considerations. To enable theory-guided development and evaluation of personality state measures, we introduce a framework based on the revised latent state-trait (LST-R) theory. The theory defines latent states as the expectation of an observed measure given a person in a specific situation, which can be decomposed into latent traits and latent situation-specific state residuals. Consequently, items and scales can be evaluated for their reliability due to latent traits (consistency) and situation-specific influences (specificity). We propose that specificity, in particular, is an appealing property for instruments designed to assess personality states. We illustrate this framework with experience sampling data on personality states. Our framework has implications for both the conceptualisation and the assessment of personality states. On the theoretical side, we provide a formal definition of personality states, which enables integration between trait-, process-, and development-focused theories. On the practical side, we show how using LST-R models allows researchers to develop and evaluate state measures on their own terms rather than applying criteria for trait measures to assess the qualities of state measures. A personality state is made up of the feelings, thoughts, behaviours, and/or desires a person experiences at a particular moment in time. Although personality is often thought of in terms of stable traits, personality states can fluctuate from moment to moment. Contemporary personality theories hold that personality traits reflect the distribution of states a person experiences over time. Despite the theoretical importance of personality states, personality (and other) researchers often lack the tools to assess states. One reason for this is the lack of a framework which can guide the development and evaluation of personality state measures. We propose such a framework. In doing so, we build on the revised latent state-trait (LST-R) theory. LST-R theory enables us to explicitly define personality states and evaluate personality state measures. In particular, we propose that personality state measures should be specific, which means that they reliably capture moment-to-moment fluctuations in personality states. We illustrate this framework by re-analysing personality states captured through experience sampling methods. Our framework has implications for both the conceptualisation and the assessment of personality states. On the theoretical side, we provide a formal definition of personality states, which enables integration between trait-, process-, and development-focused theories. On the practical side, we show how using LST-R models allows researchers to develop and evaluate measures which capture the most important properties of personality states.