The resistance against fungal decay and insect attack of wood can be highly variable, between boards and even within boards. The variability in durability is not always an issue, but for high demanding applications information about its reliability is required. This comprises the variability of outdoor performance. Durability testing in laboratory and outdoor exposures can provide a good basis to predict the overall performance of the wood material in specific applications. However, commonly only a durability class or the mean decay rating is given. Only a small number of publications are available on how to express variability in field test data. Nowadays with the availability of easy to operate powerful statistical software, advanced statistical data analysis can be done without fully understanding both, the data and the evaluation method. This can lead to wrong interpretation of the data and drawing incorrect conclusions. Therefore, it is important to know which mathematical or statistical method to use and how to interpret the results. In this paper a series of statistical methods and graphical interpretations are presented to address and visualise variability of test results. The data is obtained from an AWPA E7 field test in Thailand with Teak (Tectona grandis), Makha (Afzelia xylocarpa), and acetylated Radiata pine (Pinus radiata). 20 stakes from each material have been exposed for 5 years at 5 different test sites. The specimens were assessed every 6 months with respect to decay and termite attack.

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