ABSTRACT
At the time of writing, the role played by opinion evidence in criminal trials is the source of considerable consternation. ‘Opinion’ has been defined by the Australian courts as ‘an inference drawn or to be drawn from observed and communicable data,’1203 and this definition, though seemingly broad,would appear to bewidely accepted. As a general rule, evidence of opinion is inadmissible in criminal trials since it is the opinion of the jurors, and not thewitnesses, whichwill determine the question of guilt. As this chapter demonstrates, it can, however, be difficult to draw a neat dividing line between what constitutes fact, and what constitutes opinion. After all, we are all accustomed to expressing opinions regularly in both our professional and personal lives. Each of us will hold an opinion about what is moral or immoral, what fashion we like, what music we like, and so on. Similarly, the general practitioner may well form an opinion about what is wrong with his patient on the grounds of what is said in his surgery and the barrister will form an opinion about the client’s chances of success when he receives instructions from a solicitor. Of course, such opinions may be correct, or incorrect: a specialist consultation may reveal the general practitioner was wrong in his original diagnosis, and the barrister could eventually find the judge takes a rather different view of the strength of a particular case.
