Sometimes it is necessary to estimate the mean and/or percentile of a certain population by limited sampling, in order to compare with target values. Done properly, the method should account for random chance in the sampling. One example is the “acceptance procedure for verification of a lot” found in the standard EN 14358. This procedure is intended to be used when checking a certain population of timber (of initially unknown mean, variation and distribution) against requirements that are defined by only a mean or percentile value. Unfortunately, the procedure is confusing, with the standard giving incomplete information. This paper provides some explanation, suggests some improvements, and gives some examples with model and real data.
Keywords: strength grading, EN 14358, characteristic values, verification, non-parametric
Authors
Daniel Ridley-Ellis
Edinburgh Napier University, Scotland
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