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Standard of Proof in Court Cases
Proof beyond reasonable doubt and upon balance of probabilities
In general, the law as to standard of proof has been adopted by Papua New Guinea via the common law. It is therefore, part of the underlying law (combinations of customary law of PNG and common law). Special issues arise in relation to criminal standard of proof because of the provisions paragraph 37(4)(a) of the Constitution of Papua New Guinea, a matter discussed below.
The issue of standard of proof is separate from cogency of evidence. Witnesses may give all the necessary evidence. The witnesses may also give all necessary evidence to establish the facts in issue, but there will be no cogency to this evidence if the tribunal of facts thinks they are lying or untrustworthy.
In civil cases
The standard of proof in civil cases is ‘on the balance of probabilities’ . In a case where there is evidence of liability and it does not favour either one party or the other, the plaintiff caries the onus, and will fail unless he or she can prove his or her case on the balance of probabilities. On the basis of the principle of ‘he or she who assert must prove an affirmative defence, (e.g. contributory negligence) has to be proved by the Accused, upon the balance of probabilities.
When criminal matters are raised in civil proceedings, the standard of proof is still on the balance of probabilities, although the evidential burden of proving the criminal elements of actions will be high. This is sometimes referred to as demanding ‘strict proof’ or the ‘most cogent evidence’ etc.
The standard of proof in matrimonial causes (divorce) is laid down in the Matrimonial Causes Act section 80 of Papua New Guinea.
“Section 80(1) For the purpose of this Act, a matter of fact shall he taken to be proved if it is established to reasonable satisfaction of the court.’
In Criminal cases
In a criminal case the standard of proof required by the common law of the prosecution is beyond reasonable doubt. But if there is a legal burden for establishing a defence imposed on the Accused, it needs to be proved on the balance of probabilities.
It is notoriously difficult to define precisely what is meant by proof ‘beyond reasonable doubt.’ The problem of defining the concept arises most commonly be given by judges in jury trails of criminal offences, where explanations of the concept must commonly be given. For a discussion of the concept and the problems involved, see Murphy, (3rd ed), pp. 95 – 96) and (4th ed), pp.106 – 7).
In criminal cases, where the admissibility of a confession is challenged on the basis of voluntariness, the standard of the burden on the prosecution to establish voluntariness is beyond reasonable doubt. This issue is discussed in more detailed when we consider grounds for exclusion of relevant evidence.
Until 1991 few PNG court cases had considered the nature of criminal standard of proof. There was comment on its continuing appropriateness in PNG in the case of.
As common law requirements, it might have been that both the criminal and civil standards of proof could be open to question under Schedule 2 of the Constitution of Papua New Guinea as subject to custom, being in appropriate to PNG, etc. Alternatively, they could be changed by statute. These issues were never seriously argued – though in relation to criminal standard, Prentice Dept. CJ (as he then was) in the case of The State v John Koe (as per mentioned above), indicated the criminal standard continued to be appropriate.
In the 1991 decision of the majority in the Supreme court in SCR No. 2 of 1990, it was decided that although the criminal standard of proof was imposed into PNG via the underlying law through the requirement of proof of “guilt according to law”. Proved for in paragraph 37(4)(a) of the Constitution together with its incorporation PNG law through a constitutional provision gave it special status. The majority found that the criminal standard of proof (and other aspects of criminal procedure) had been elevated to constitutional rights status, and cannot be altered by ordinary status.
 Murphy (3rd ed) pp.99 – 101 and 4th ed. Pp.111 – 113) for a discussion of what the concept means.
 See in the case of The State v Allan Woila  PNGLR 99.
 The State v John Koe  PNGLR 562 at page 564