International audienceThis paper reports on methodological results from an ongoing project investigating student transition from teacher education to the world of work. We argue that research benefits from purposeful sampling, and we present two Rasch-calibrated instruments that aim at finding participants with particular characteristics. With items from existing instruments, one practice instrument is calibrated on Norwegian student teachers. Furthermore, these items are rephrased to fit a second instrument measuring beliefs about teaching mathematics. Finally, 'virtual equating' is used to align items so that measures can be compared across instruments