2.3 Rule 3: there are at least 10 occurrences in each year

An occurrence is non-zero observation at unique combination of site, point and date. When there are less than 10 of those occurrence in a year for a given species, then that species is too rare to fit a stable model.

Note that some species have no occurrences or few occurrence during the early years and more data from later years (tab. 2.3). Therefore we apply the rule to the most recent year first. If the year we are checking has at least 10 occurrences, we check the earlier year. Otherwise we stop the check and keep only the more recent years. This rule keeps 84 out of the remaining 130 species.

Table 2.3: Number of occurrences per year. Period with at least 10 occurrences per year. Number of relevant occurrences with the period.