Tendency and coincidence evidence 

Some of the most contentious admissibility disputes in Australian courts concern evidence that a person has behaved a particular way before, or that a suspicious pattern of events is too improbable to be coincidence. This evidence can be powerfully probative, and it can also be powerfully unfair. The law's response is a deliberately cautious, heightened threshold for admitting it.

Tendency evidence

Tendency evidence is evidence that a person has, or had, a tendency to act in a particular way, or to have a particular state of mind, tendered to prove that the person acted, or thought, consistently with that tendency on the occasion in issue. Hughes v The Queen (2017) 263 CLR 338¹ confirms this is only admissible where the tendency evidence has the significant probative value the legislation requires. Typical examples include evidence of prior conduct offered to show that a person was disposed to behave the same way again, or evidence of a settled attitude or intention offered to show the person held that attitude at the relevant time. The reasoning is inferential: because a person has behaved a certain way before, or holds a certain disposition, it becomes more likely they behaved consistently with it on the occasion the case is actually about.

One category of case in New South Wales is no longer decided that way. Section 97A of the Evidence Act 1995 (NSW)², inserted in 2020, applies where the commission of a child sexual offence is a fact in issue, and presumes that tendency evidence about the defendant's sexual interest in children — "even if the defendant has not acted on the interest" — has significant probative value for ss 97(1)(b) and 101(2). The presumption applies whether or not the interest was directed at a complainant in the proceeding. A court may still find the evidence lacks significant probative value where there are sufficient grounds, but s 97A(5) takes seven matters out of that assessment absent exceptional circumstances — including that the tendency act differs from the act alleged. Identify whether s 97A applies before running the ordinary assessment.

Coincidence evidence

Coincidence evidence operates on a related but distinct logic. It is evidence that two or more events occurred, tendered on the basis that it is improbable they occurred coincidentally, in order to prove that a person did a particular act or had a particular state of mind. Rather than reasoning from a general disposition, coincidence reasoning asks the fact-finder to infer a fact from the sheer unlikelihood that a particular combination or repetition of events would occur by chance, given some common feature connecting them.

The two categories often arise together on similar facts — evidence capable of showing a tendency can also form part of a coincidence argument — but they rest on different inferential logic and are treated as distinct rules with their own conditions.

Why both are treated with caution

The danger both rules exist to control is prejudicial propensity reasoning: the risk that a fact-finder, once told a person has behaved badly before or fits a suspicious pattern, will reason that the person is simply the "type" to have done the act in question, and convict or find liability on that basis, rather than on the strength of evidence that the person actually did the specific thing alleged on this occasion. This kind of reasoning can be seductive precisely because it feels intuitive, while being logically weak and unfairly loading the scales against a party — particularly an accused in a criminal trial, whose whole prior history or character can otherwise become the true subject of the fact-finder's attention instead of the conduct actually charged.

Because of that risk, both tendency and coincidence evidence are subject to a heightened admissibility threshold beyond ordinary relevance. Rather than being received merely because it is capable of rationally affecting the assessment of a fact in issue, this evidence is typically required to reach a materially higher level of probative value before it is admitted, and the balancing of that probative value against the risk of unfair prejudice is applied more strictly than for evidence generally — particularly where the evidence is tendered against an accused in a criminal proceeding. The precise formulation of that heightened threshold, and the procedural safeguards (such as notice requirements) that commonly accompany it, differ between the uniform evidence law and the non-uniform jurisdictions, but the underlying caution is a consistent feature of Australian evidence law.

Working through a tendency or coincidence problem

The recurring task is to identify precisely what inference the evidence is being used to support, and to test whether that inference depends on disposition (tendency) or on the improbability of coincidence (coincidence), before turning to whether the heightened threshold is met. It is also important not to dismiss such evidence as automatically inadmissible: where its probative value is genuinely high — for example, because of a distinctive and unusual common feature linking separate events — the heightened threshold can be satisfied, and the evidence admitted notwithstanding the caution that surrounds this category.

Hughes is narrower than it reads on identity. In TL v The King (2022) 276 CLR 140³ the Court held at [30] that the "close similarity" observation "should be understood as postulating a situation in which there is little or no other evidence of identity apart from the tendency evidence, and the identity of the perpetrator is 'at large'", and at [38] that where other identification evidence was strong the threshold "was capable of being met without the close similarity insisted upon by the appellant".

Applying this in a problem question

1. Identify whether the evidence is being used to show a disposition (tendency) or the improbability of a pattern of events occurring by chance (coincidence), or both.
2. Articulate the precise inferential chain from the evidence to the fact in issue, and assess its genuine probative value on the specific facts.
3. Apply the heightened admissibility threshold rather than ordinary relevance, and weigh probative value against the risk of unfair prejudice with particular care.
4. Consider whether the evidence risks inviting prejudicial propensity reasoning distinct from its legitimate probative use, and whether that risk can be managed.
5. Identify the jurisdiction and note that the specific threshold and any notice requirements differ between the uniform evidence law and Queensland, South Australia and Western Australia.