The need to develop tools to assess and support the of space-dwelling crews continues to be acknowledged by NASA (Suedfeld, Bootzin, Harvey, Leon, Musson, Oltmanns, & Paulus, 2010). In that regard, the term behavioral health encompasses a broad range of affective, social, and skilled individual and crew performances that must be sustained under the obviously stressful circumstances of long-duration spaceflight (Brady, 2007; Emurian & Brady, 2007). The detection of impending performance degradation necessitates the consideration of innovative approaches to monitor and measure both individual and team performances that realistically relate to the operational status of a crew. The introduction of effective countermeasures to such degradation is complementary to detection, and potential solutions to these two challenges will benefit from a technology that can integrate both considerations within a common conceptual framework with respect to task performance. A three-person team performance task (TPT) was proposed as a tool to diagnose the status of a crew (Emurian, Canfield, Roma, Gasior, Brinson, Hienz, Hursh, & Brady, 2009), and the rationale of its design, from the perspective of behavior analysis, and an evaluation of its effectiveness have been reported (Emurian, Canfield, Roma, Brinson, Gasior, Hienz, Hursh, & Brady, in press). The initial evaluations were based upon having subjects perform the task for fixed time periods (e.g., 12 min), with instructions to maximize performance effectiveness. Although providing important feedback regarding the properties of the task and performance metrics associated with individual and team performances, a more realistic diagnostic scenario would require a crew to complete a given task without regard to temporal constraints. Accordingly, the present extension of the task implements a fixed-ratio requirement on performance accuracy at the level of the individual team member and at the level of the team. The present report is a case study of the evaluation of such an extension under conditions of the replacement of an established team member with a novitiate. The context of this study includes analyses of group membership replacement previously undertaken within a continuously programmed environment (Emurian,Brady, Ray, Meyerhoff, & Mougey, 1984). Method Subjects Four UMBC undergraduate students volunteered to participate in response to an announcement posted on the student listserv. Volunteers were directed to read the information posted on the web (http://nasa1.ifsm.umbc.edu/tpt/). The study was approved by UMBC's Institutional Review Board, and informed consent was obtained at the time of each daily session. Each participant was paid $30 in cash at the completion of a session. Table 1 presents demographic details about the four subjects collected before Session 1 for subjects 1, 2, and 3 and before Session 5 for subject 2*. Two rating scales were administered to assess each subject's experience with computer games and overall computer experience. Each scale was a 10-point scale, where the anchors were 1 = No Experience (I am a novice.) to 10 = Extensive Experience (I am an expert.). Notable, perhaps, are the comparatively low ratings by S2 for both game and computer experience. Subjects 1, 2, and 3 reported being acquainted prior to the study. Subject 2 was replaced at Session 5 of the study by S2*, and the replacement reported having no prior acquaintanceship with the other two subjects. The subjects were instructed not to discuss the task between sessions, and post-session debriefings always confirmed that practice. Team Performance Task (TPT) The TPT was designed for use by three-person groups, and the prototype has been described in detail elsewhere (Emurian et al., in press). Figure 1 presents a screen shot of the display presented to a subject (in this case, User1, the designation for S1). …