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An important element in scenario-based architecture evaluation is the development of scenario profiles by stakeholders working in groups. In practice groups can vary in size from 2 to 20 people. Currently, there is no empirical evidence about the impact of group size on the scenario development activity. Our experimental goal was to investigate the impact of group size on the quality of scenario profiles developed by different sizes of groups. We had 165 subjects, who were randomly assigned to 10 groups of size 3, 13 groups of size 5, and 10 groups of size 7. Participants were asked to develop scenario profiles. After the experiment each participant completed a questionnaire aimed at identifying their opinion of the group activity. The average quality score for group scenario profiles for 3 person groups was 362.4, for groups of 5 person groups was 534.23 and for 7 person groups was. 444.5. The quality of scenario profiles for groups of size 5 was significantly greater than the quality of scenario profiles for groups of size 3 (p=0.025), but there was no difference between the size 3 and size 7 groups. However, participants in groups of size 3 had a significantly better opinion of the group activity outcome and their personal interaction with their group than participants in groups of size 5 or 7. Our results suggest that the quality of the output from a group does not increase linearly with group size. However, individual participants prefer small groups. This means there is a trade-off between group output quality and the personal experience of group members.