OSCEs require large numbers of examiners: this can be strength, as candidates are observed and scored by clinicians, but also one of its potential weaknesses, as inconsistency between examiners will reduce the fairness and reliability of an OSCE.
Considerable resources should be devoted to examiner training. Training sessions should cover the principles of OSCEs and the role of examiners i.e. to assess and not to teach or conduct vivas, to adhere to marking schedules, and respect the role of the simulated patient. Training can usefully involve both the marking of pre-recorded or role-played OSCE stations, after which the marking is reviewed with the clinicians.