This experiment investigated the use of positive and negative hypothesis and target tests by groups in an adaptation of the 2-4-6 Wason task. The experimental variables were range of rule (small vs large), amount of evidence (low vs high), and trial block (1 vs 2). The results were in accordance with Klayman and Ha's (1987) analysis of base rate probabilities of falsification and with additional theoretical considerations. Base rate probabilities were more descriptive of participants' behaviour in target than in hypothesis (...) tests, under low than under high amount of evidence, and at the beginning of the process than at its end. The percentage of positive tests was higher under small than large range of rule. More falsifications than verifications resulted from hypothesis tests than would be expected by a random process. When evidence is richly available, the relative importance of falsification seems to decrease. An analysis of the group compositions before and after group discussion by the PCD model (Crott, Werner, & Hoffmann, 1996) revealed that the normative weight was approximately twice as large as the informational. Groups produced fewer false answers than their members individually. (shrink)