82 Preparation Group composition is another specialized group formation task in the preparatory phase. At minimum, prospective members need to have com- mon concerns and interests—a commonality of purpose. The social worker must consider the desired range of commonness or difference on important background and personality factors. The worker must determine whether the “same-ness” of the experience will override its “different-ness.” The worker can also be guided by the Noah’s Ark principle, which holds that whenever possible, each member of a group should share with at least one other member charac- teristics that are considered central to the group’s work. A parallel principle is “not the only one,” which suggests that no one should stand out as the sole member with a characteristic that is relevant to the group’s work. Group purpose, type of group, and organizational context all influence the group’s temporal arrangement. Most groups are planned and short term. Time limits help members focus quickly and maintain their purpose, direction, and sense of urgency and have been found to enhance their motivation and com- mitment to work. In some situations, as the group nears completion and evalu- ates its progress, members and the worker may decide to recontract for another cycle or a specific number of additional sessions. In time-limited group services, the worker clearly identifies the ending date in the first session. Certain settings, such as schools, have a natural time frame based upon the academic year, which groups are likely to follow. Religious hol- idays, winter and spring breaks, and the end of the school year provide natural benchmarks to either end the group or to evaluate progress and determine if additional time is needed. Other considerations are the frequency and duration of sessions, which should be arranged in ways that are responsive to the unique needs of the population being served. Another consideration is group size. Appropriate group size is related to group purpose and type. Generally, larger groups (approaching 20 members) will need to become more formalized. Communication may have to be chan- neled through the designated leader, with limited opportunity for individual attention, accessibility to the worker, and intimate, spontaneous participation. Because community groups are designed for social action and depend upon “power in numbers,” large numbers of members are preferable. For most of the groups that social workers are likely to lead, group size typi- cally ranges from as many as 12–15 members to as a few as 4–5. For some clients, such as those with chronic mental illness, young children, or the frail elderly, large groups may be overstimulating and confusing, leading to withdrawal and isolation. Clients who are shy, withdrawn, or socially isolated might find a larger group intimidating, which may undermine their ability to benefit from participation. Smaller groups offer greater opportunity for individualization, providing each member with sufficient time and accessibility to peers and the worker. A moderately sized group (approximately 6–8 members) is likely to be