Investigating Heterogeneity in Response Strategies: A Mixture Multidimensional IRTree Approach

To improve the validity of self-report measures, researchers should control for response style (RS) effects, which can be achieved with IRTree models. A traditional IRTree model considers a response as a combination of distinct decision-making processes, where the substantive trait affects the decision on response direction, while decisions about choosing the middle category or extreme categories are largely determined by midpoint RS (MRS) and extreme RS (ERS). One limitation of traditional IRTree models is the assumption that all respondents utilize the same set of RS in their response strategies, whereas it can be assumed that the nature and the strength of RS effects can differ between individuals. To address this limitation, we propose a mixture multidimensional IRTree (MM-IRTree) model that detects heterogeneity in response strategies. The MM-IRTree model comprises four latent classes of respondents, each associated with a different set of RS traits in addition to the substantive trait. More specifically, the class-specific response strategies involve (1) only ERS in the ERS only class, (2) only MRS in the MRS only class, (3) both ERS and MRS in the 2RS class, and (4) neither ERS nor MRS in the 0RS class. In a simulation study, we showed that the MM-IRTree model performed well in recovering model parameters and class memberships, whereas the traditional IRTree approach showed poor performance if the population includes a mixture of response strategies. In an application to empirical data, the MM-IRTree model revealed distinct classes with noticeable class sizes, suggesting that respondents indeed utilize different response strategies.

Automated summary

To improve the validity of self-report measures, researchers can use IRTtree models to control for response style effects. Traditional IRTtree models assume that all respondents use the same response style, while a new mixture multidimensional IRTtree model takes into account heterogeneity in response strategies. In an application to empirical data, the new model reveals distinct response strategy classes.