With regard to the second issue, the court rejected Cumbria’s initial position that its sample evidence could be extrapolated with a 95% confidence rate across the whole of the works. The court noted that it was well understood by statisticians that this level of confidence could only be demonstrated mathematically if the sample evidence was obtained by a genuinely random sampling process. Cumbria ultimately accepted that its sample was not sufficiently random and, whilst this ruled out proof of a 95% rate of confidence, the court found that there was no principle of law or statistical theory to suggest that such a claim could only be established by statistically random sampling. Cumbria was therefore entitled to rely upon its sample evidence but was required to demonstrate that, whilst it may not be statistically random, it was still sufficiently representative of the whole of the works. Ultimately, Cumbria failed to show that its sample evidence was sufficiently representative: • The sample was initially obtained to ascertain the presence or absence of defects and not a general sample of the works carried out by Amey. Accordingly, the sample was not being used for the intended purpose of its collection. • The sampling process had been extended over a lengthy period of time. • Patches from the sample which could not be located on a GPS were excluded from the statistical analysis, thereby excluding samples from works carried out earlier in the project before GPS was being used. • The sample excluded patches classified as “pre-surface dressing patches” which had subsequently been covered by surfacing. The court held that each of these matters demonstrated an opportunity for the sample to be infected with bias. Cumbria was also found to have failed to have proper processes for collection of the sample and did not take suitable steps to mitigate and/or avoid the possibility of bias. In these circumstances, it was held that it would be unsafe to extrapolate the sample evidence relied upon by Cumbria. Conclusions and implications This case provides important guidance for the bringing of representative defects claims under construction contracts. The need for such claims can arise wherever a construction project involves repetitive work, such as welding, bricklaying, glazing or road repairs as in the present case. Although it will always be preferable for a claimant to prove each item of defective work, the present case shows that where this is impractical or impossible, evidencing a claim by reference to a statistically random or sufficiently representative sample will be permissible. The difficulties involved in doing so should not be underestimated, however. Care is needed from the outset to ensure any sample evidence collected is genuinely random and/or sufficiently representative and that all possible steps are taken to avoid the sample being affected by bias. References: Amey LG Limited v Cumbria County Council [2016] EWCH 2856 (TCC)
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