Sharing information with other group members is associated with group member perceptions of competence, knowledge, and credibility (Wittenbaum & Park, 2001). According to Broderick, Kerschreiter, Mojzisch, and Schulz-Hardt (2007), information known to only a single member of a group prior to group discussion will be mentioned less often and evaluated less favorably compared with information known to multiple group members prior to a group discussion.This phenomenon describes shared information bias (Baker, 2010). Shared information bias (also known as the collective information sampling bias) is thus a tendency for group members to spend more time and energy discussing information that multiple members are already familiar with (i.e., shared information). Researchers predict poor decision-making can arise when the group does not have access to unshared information for making well-informed decisions. The result of inaccessible unshared information is called hidden profiles. Hidden profiles describe group decision tasks in which different (but correct) possible solutions exist, but no group member detects it based on his or her individual information prior to the discussion (Stasser, 1988).

Causes

Although discussing unshared information may be enlightening, groups are often motivated to discuss shared information in order to reach group consensus on some course of action. According to Postmes, Spears, and Cihangir (2001), when group members are motivated by a desire to reach closure (e.g., a desire imposed by time constraints), their bias for discussing shared information is stronger. However, if members are concerned with making the best decision possible, this bias becomes less salient.^[4] Stewart and Stasser (1998) have asserted that the shared information bias is strongest for group members working on ambiguous, judgment-oriented tasks because their goal is to reach consensual agreement than to distinguish a correct solution.^[5]The shared information bias may also develop during group discussion in response to the interpersonal and psychological needs of individual group members. For example, some group members tend to seek group support for their own personal opinions. This psychological motivation to garner collective acceptance of one’s own initial views has been linked to group preferences for shared information during decision-making activities (Greitemeyer & Schulz-Hardt, 2003; Henningsen & Henningsen, 2003)^[6][7]Lastly, the nature of the discussion between group members reflects whether biases for shared information will surface. According to Wittenbaum et al. (2004), members are motivated to establish and maintain reputations, to secure tighter bonds, and to compete for success against other group members.^[8] As a result, individuals tend to be selective when disclosing information to other group members.

Outcomes

Wittenbaum, Hubbell, and Zuckerman (1999) examined mutual enhancement during various discussions about job candidates (i.e., interactions between two people). Participant dyads were assigned to one of two conditions. Before meeting to discuss candidate profiles, researchers had dyads in the first condition look at same information about candidates, while the second condition had dyads receive different information. Participants in condition one evaluated both their partner and self as more component and credible.

Avoidance strategies

Several strategies can be employed to reduce group focus on discussing shared information:

• Make effort to spend more time actively discussing collective decisions. Given that group members tend to discuss shared information first,^[9] longer meetings increase likelihood of reviewing unshared information as well.
• Make effort to avoid generalized discussions by increasing the diversity of opinions within the group (Smith, 2008).
• Introduce the discussion of a new topic to avoid returning to previously discussed items among members (Reimer, Reimer, & Hinsz, 2010).^[10]
• Avoid time pressure or time constraints that motivate group members to discuss less information (Kelly & Karau, 1999; Bowman & Wittenbaum, 2012).^[11][12]
• Clarify to group members when certain individuals have relevant expertise (Stewart & Stasser, 1995).^[13]
• Include more group members who have task-relevant experience (Wittenbaum, 1998).^[14]
• Technology (e.g., group decision support systems, GDSS) can also offer group members a way to catalog information that must be discussed. These technological tools (e.g., search engines, databases, computer programs that estimate risk) help facilitate communication between members while structuralizing the group’s decision-making process (Hollingshead, 2001).