Abstract
The purpose of this paper is to analyze the behaviour of the lognormal distribution function in wave studies, when visual observations are used to predict the long term wave height distribution. We are focused our attention on the problem of visual biased samples. For this kind of data the lognormal model does not fit accurately the sample leading to wrong extrapolations. One possible solution to avoid this problem is to consider the sample as truncated. According to this procedure the distribution function is estimated based only on data higher than the point of truncation.
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