  Recent work has looked to understand user perceptions of speech agent
capabilities as dialogue partners (termed partner models), and how this affects
user interaction. Yet, currently partner model effects are inferred from
language production as no metrics are available to quantify these subjective
perceptions more directly. Through three studies, we develop and validate the
Partner Modelling Questionnaire (PMQ): an 18-item self-report semantic
differential scale designed to reliably measure people's partner models of
non-embodied speech interfaces. Through principal component analysis and
confirmatory factor analysis, we show that the PMQ scale consists of three
factors: communicative competence and dependability, human-likeness in
communication, and communicative flexibility. Our studies show that the measure
consistently demonstrates good internal reliability, strong test-retest
reliability over 12 and 4-week intervals, and predictable convergent/divergent
validity. Based on our findings we discuss the multidimensional nature of
partner models, whilst identifying key future research avenues that the
development of the PMQ facilitates. Notably, this includes the need to identify
the activation, sensitivity, and dynamism of partner models in speech interface
interaction.
