State Government Insurance Commission v Laube has been followed in Payne v Crawford (1992) 3 Tas R 360 (per Zeeman J) and R v Mitchell (1997) 130 ACTR 48 (per Higgins J).
137 In my respectful opinion, it is overstating the position to say that, as an absolute proposition, "the statistical fact that a particular proposition is true of the majority of persons cannot of itself amount to legal proof on the balance of probabilities that the proposition is true of any given individual". In my opinion, the matter is essentially one of degree. This is demonstrated by Spigelman CJ's discussion of epidemiological evidence in Seltsam Pty Ltd v McGuiness. In that case the Chief Justice considered in depth the use that may be made of epidemiological evidence in establishing causation.
138 Seltsam Pty Ltd v McGuiness (at [89], [98], and [153]) EMI Australia Ltd v BES [1970] 2 NSWR 238 at 242 (appeal dismissed (1970) 44 ALJR 360); and Fernandez v Tubemakers of Australia Ltd [1975] 2 NSWLR 190 at 239, 240 are authority for the proposition that evidence of epidemiological studies is circumstantial evidence which may, alone, or in combination with other evidence, establish causation in a specific case. The fact that experts do not infer causation on a balance of probabilities does not mean that a court may not: Seltsam Pty Ltd v McGuiness at [143]-[144]. A finding of causal connection may be made even when the expert evidence does not rise above the possible; the question is always whether the evidence as a whole establishes causation on a balance of probabilities: Seltsam Pty Ltd v McGuiness at [89], [94]-[96], [98]-[100], [102], [143], [144] and [153].
139 What is meant by "balance of probabilities" in this context? Guidance may be obtained from the remarks of Mahoney JA in Jones v Sutherland Shire Council [1979] 2 NSWLR 206 where his Honour, in commenting on this issue, said (at [227]):
"The first step, in a sense, involves simply an assessment of what is human experience: it is, or is not, a fact that human experience is so. But such an assessment is not made as a mathematical calculation. It involves other kinds of reasoning in judgments, the correctness of which cannot be demonstrated by mathematics or ordinary logic. Therefore, the subjective confidence which a person or a court will have in the correctness of the assessment may vary.
It is to this that, in my opinion, phrases such as 'the balance of probabilities' refer in respect of such an assessment."
140 Mahoney JA observed that one possible meaning of a thing being "probable" is where the person, judging the probability of that thing, "has the appropriate degree of confidence in its existence or correctness based on or judged according to reason". His Honour remarked (at [227-228]):
"It is in this sense that 'probability' is used in determining whether a particular proposition of fact should be accepted for the purpose of litigation. It was in my opinion to this that Dixon J referred in Briginshaw v Briginshaw [1938] HCA 34; (1938) 60 CLR 336 at 361. In referring to what constituted proof of a fact, his Honour said: ' … the tribunal must feel an actual persuasion of its occurrence or existence before it can be found. It cannot be found as a result of a mere mechanical comparison of probabilities independently of any belief in its reality'."
141 These observations echo his Honour's remarks in Fernandez v Tubemakers of Australia Ltd at 199 (quoted by Spigelman CJ in Seltsam Pty Ltd v McGuinness at [95] and [99]) and with respect, are not inconsistent with what is said in Flounders v Millar at [35], namely:
"It remains necessary for a plaintiff, relying on circumstantial evidence, to prove that the circumstances raise the more probable inference in favour of what is alleged. The circumstances must do more than give rise to conflicting inferences of an equal degree of probability or plausibility. The choice between conflicting inferences must be more than a matter of conjecture. If the court is left to speculate about possibilities as to the cause of the injury, the plaintiff must fail. … The rules governing causation at common law are those expressed in Luxton v Vines and March v Stramare (E & M H) Pty Limited , namely, the test of commonsense, with the onus of proof at all times being on the plaintiff".
142 Mr Menzies submitted, in effect, that the fact that, epidemiologically, 62 per cent of persons who had breast cancer such as Mrs O'Gorman had in March 2006 would not have experienced any metastatic effect had that cancer been detected and treated at that time, does not prove that Mrs O'Gorman was not part of the 38 per cent who would have experienced metastasis, in any event.
143 It is not necessary to decide whether this submission is correct as there is other, additional evidence on which the appellant relies to establish causation, namely, the increase in the risk of metastasis by 10 per cent that occurred between March 2006 and January 2007.
144 Statistically speaking, Mrs O'Gorman had a 62 per cent chance of not experiencing metastasis. That being so, I would comment (without deciding the issue) that it is reasonably arguable - on a common sense basis - that if 62 persons out of 100 in Mrs O'Gorman's position would not have experienced metastasis had the cancer been detected and treated in 2006, it is probable that Mrs O'Gorman's cancer would not have metastasised had it been detected and treated in March 2006.
145 I would add that, while this statistic does not necessarily establish proof on a balance of probabilities (although it arguably does), in my opinion - at the very least - it shows that there was a strong possibility that, had the tumour been detected in March 2006, Mrs O'Gorman's cancer would not have metastasised. On this ground alone, this case is materially different from Gett v Tabet.
146 The evidence that the failure to diagnose increased the risk of metastasis by 10 per cent between February 2006 and January 2007 is another strand in the causation cable. For the reasons I have previously given, I shall first deal with the effect of that evidence on the basis that it is not epidemiological evidence but evidence that the risk to Mrs O'Gorman, as an individual, increased by 10 per cent. That is on the basis that it is not now open to the appellant to resile from its acceptance that there was an increase in the risk to Mrs O'Gorman personally and not as a member of a segment of the population.
147 Evidence of the increase by 10 per cent of the risk to Mrs O'Gorman as an individual is of particular significance as it is not epidemiological evidence but is evidence that applies, singularly, to Mrs O'Gorman. This evidence further differentiates this case from Gett v Tabet. Whether this evidence does in fact prove causation is a matter of evaluative judgment based on the criteria referred to in Luxton v Vines (1952) 85 CLR 352, March v Stramare (E & M H) Pty Limited [1991] HCA 12; (1991) 171 CLR 506, Fernandez v Tubemakers of Australia Ltd, Seltsam Pty Ltd v McGuiness, EMI (Australia) Ltd v BES, and Jones v Sutherland Shire Council.
148 As I have stated, there was, at least, a strong possibility that, had the radiologists detected the tumour, it would not have metastasised. Not a great deal of evidence would be required to tip the scales from that strong possibility to a finding that, on a balance of probabilities, the failure to detect the tumour led to the metastasis.
149 The increased risk to Mrs O'Gorman as an individual made it more likely that the tumour would metastasise and the risk was increased to an extent that was not negligible. In my opinion, that evidence is significant and is sufficient to tip the scales. By the failure to detect and treat Mrs O'Gorman's cancer, the risk of metastasis increased by about 10 per cent, not statistically but personally to her. She was directly rendered more susceptible to metastasis. In my opinion, applying the common sense test of causation, I am satisfied that the failure in March 2006 to detect and treat the cancer caused the metastasis.
150 I now turn to the same issue but on the basis that the evidence as to an increase in the risk was not evidence that applied to Mrs O'Gorman personally, but was epidemiological evidence.
151 The starting point, again, is the fact that epidemiological evidence is only evidence of possibility. I repeat, however, that epidemiological evidence may alone establish causation in a specific case.
152 Assume that epidemiological evidence shows that is a 99 per cent chance that no metastasis will result from a detected and treated tumour (and the prospect that metastasis would occur in any event is one per cent). In my view, that evidence alone would establish causation where there was a failure to detect a tumour and metastasis followed.
153 The statistical position in the present case is that in March 2006 the prospect of metastasis not occurring (had the tumour been detected and treated) was 62 per cent. I have found that that evidence establishes, at the least, a strong possibility that, had the tumour been detected in March 2006, no metastasis would have occurred. The question is whether the increased epidemiological risk of Mrs O'Gorman experiencing metastasis because of the failure to detect the tumour is sufficient to convert the strong possibility into a probability.
154 In my view, that question must be answered in the affirmative. This is essentially an evaluative decision based on common sense. I can express the reasoning behind my conclusion no better than by paraphrasing Mahoney JA's remarks in Fernandez v Tubemakers of Australia Ltd (at 200). I consider that the evidence showed that the connection between the appellant's negligence and the subsequent tumours that metastasised was sufficiently close to warrant a reasonable mind concluding on a balance of probabilities that the appellant's negligence was the actual cause of the tumours that metastasised.
155 I would therefore dismiss the appeal against the decision as to causation.