The ability to carry out an investigation and to collect data without personal interpretation or bias to influence the process. If we have to rely on a subjective interpretation of an event (such as 'Was that an act of aggression or of playfulness'?), we may find it difficult to maintain our objectivity. Psychologists may choose either to concentrate on actions which are unquestionably relating to the behaviour of interest (stabbing someone in the back, for example, could hardly be interpreted as playfulness) or relying on the shared agreement of more than one observer of the same event (inter observer reliability).