Results for the two preliminary rounds are summarized in Table . As a measure for inter-rater agreement, we consider the Fleiss' κ F coefficient among the responses provided by the chemists in both preliminary rounds. We measured κ F 1 = 0.4 and κ F 2 = 0.32 for the first and second round, respectively, and concluded that there was a moderate agreement between the preferences expressed by the chemists. One likely reason for the only moderate agreement is the fact, that especially in cases where there is no clearcut preference, decisions were be driven by prior per-Table : Intra-rater agreement, as measured by the percentage of times chemists agreed with their previous choice on a pair and by the Cohen's κ coefficient. Left-right bias measured as the percentage of times a rater chose the compound presented on one side of the screen. Abbreviations: R1/R2: First/second preliminary round of the study Intra-rater Ag.