We present an extensive empirical evaluation of collocation extraction methods based on lexical association measures and their combination. The experiments are performed on three sets of collocation candidates extracted from the Prague Dependency Treebank with manual morphosyntactic annotation and from the Czech National Corpus with automatically assigned lemmas and part-of-speech tags. The collocation candidates were manually labeled as collocational or non-collocational. The evaluation is based on measuring the quality of ranking the candidates according to their chance to form collocations. Performance of the methods is compared by precision-recall curves and mean average precision scores. The work is focused on two-word (bigram) collocations only. We experiment with bigrams extracted from sentence dependency structure as well as from surface word order. Further, we study the effect of corpus size on the performance of the individual methods and their combination.