Many medical faculties from all over the world have implemented problem-based learning (PBL). In the implementation, all educational program components, including teachers, should be consistent with student-centred teaching and learning behaviours . However, studies showed that many teachers tend to use teacher-centred approaches and do not properly facilitate students’ learning in PBL. They have difficulties moving away from the hierarchical student-teacher relationship [2–5].
One reason for teachers not showing desired behaviours in PBL is related to their teaching perspectives. Teachers with a teacher-centred perspective are assumed to have difficulties showing student-centred approaches. Therefore, institutions need to identify teachers’ teaching perspectives. Only then the institutions can remove the obstacles to the effective implementation of PBL, for example, through faculty development . An appropriate instrument to measure the teaching perspectives is necessary with attention to all aspects that influence student-centred versus teacher-centred behaviour. This reported study aims to validate an instrument that will help the institutions recognise teachers’ barriers in showing student-centred behaviours.
To perform student-centred behaviour in PBL is challenging for teachers with a teacher-centred perspective because newly required behaviour is not in line with their convictions . Pratt et al.  pointed out that a teaching perspective is a teacher's view about teaching in which the interrelation of beliefs and intentions provides direction and justification for actual behaviour. It means that teachers with a student-centred perspective tend to show student-centred behaviour. They focus on student development and student-centred learning. Conversely, teachers who have a teacher-centred perspective tend to take a teacher-centred approach. They focus on their task to transmit knowledge based on the syllabus or textbook without acknowledging the student's experiences and understanding .
Korthagen  pointed out six aspects (environment, behaviour, competencies, beliefs, identity, and mission) that contribute to teachers’ perspectives, showing that both the environment and personal characteristics influence behaviours. These six aspects, including the behaviour itself, are structured as the six layers resembling a sliced onion, in the so-called Onion Model (Figure 1). The Onion Model illustrates that the inner levels influence the outer levels and vice versa (from outside to inside).
The teaching perspectives relating to the environment refer to the external side that the teacher encounters in his/her institution, such as support from a leader and departmental peers, the number of students in a small PBL group, teaching and learning facilities, institutional rewards for teachers, and opportunities for personal development [11, 12, 13]. Behaviour refers to the teaching activities in small PBL group sessions, such as the stimulation of constructive/active learning, self-directed learning, contextual learning, and the collaborative learning of students . Competencies refer to the knowledge, skills, and attitudes of teachers for stimulating and asking questions, providing information, observing and analysing, and providing feedback . Beliefs refer to the teaching and learning values of teachers with regard to student learning in small group discussions (16). Identity refers to how the teacher defines or sees his/her professional identity as didactic and pedagogical expertise [17, 18]. Mission, finally, refers to a teacher's personal and professional aims and aspirations, such as care for the whole person, temperance, and humility .
Paying attention to these six aspects in measuring the teaching perspectives of teachers might help educational institutions identify obstacles that teachers face and recognise faculty development needs. To function properly in PBL, teachers' teaching perspectives, as measured by those six aspects, should be in a student-centred direction. When one or more of the aspects show a teacher-centred direction, they indicate an obstacle to performing student-centred behaviours. This finding will help educational institutions recognise the needs of individual teachers and, especially, how faculty development might help address those needs .
Instruments that use the Onion Model as their theoretical framework for measuring teachers' teaching perspectives do not yet exist. Previous instruments to measure teachers’ teaching perspectives, such as the Learning Inventory , the Approaches to Teaching Inventory (ATI) , the Teaching Perspectives Inventory (TPI) , and the Conceptions of Learning and Teaching (COLT)  focused on only a few of these relevant aspects, such as student learning, teacher learning, teaching approach, or teachers' uncertainty. That is problematic because the sole focus on teaching and learning processes might lead institutions to implement faculty development programs that neglect the required transformation of teachers’ beliefs, identity, and mission [6, 22].
A new instrument named Student-Centred Perspectives on Teaching (SCPT) is proposed based on the Onion Model's six levels to measure teachers' teaching perspectives. A sound instrument should have acceptable internal and external validity. Internal validation of the questionnaire will be conducted to confirm that the SCPT can quantitatively measure teachers' teaching perspectives based on the six aspects, the convergence or the sharing proportion of the items within a subscale, and the distinction of a subscale from other subscales. In addition, external validation will be conducted to provide evidence that the SCPT can distinguish teachers' teaching perspectives based on the six aspects according to the amount of PBL training they have been involved in. Therefore, the research question is: what is the evidence to support the internal and external validity of the SCPT?