Given that it is infrequent for MWEs from the same collocation (same first and last word) to be present in the gold standard, extracting more than one pattern per collocation, as SIGMA does, is penalizing for the precision with respect to our gold standard.
still, a quick manual check of the false positives reveals that most of the extracted patterns are actually correct, in that they are variants of the first pattern, such as: if a more flexible comparison is applied, such as allowing for edit distance (Damerau, 1964) up to 3 between the strings, these variants are recognized as true positives and for sIGMA improves by 10 points, as is shown in the fourth column of table 2.