In recent decades, psychologists have increasingly turned to evidence-based practice (EBP) to guide their treatments with clients. Practice-based evidence (PBE) is one type of EBP that allows clinicians to treat their clients in a flexible, but effective way. PBE treatments are those that use information gathered about the client through measures or questionnaires to inform the clinical decisions therapists make in the process of treating the client. The use of PBE in group psychotherapy is increasing and there are many measures that can potentially be used to aid therapists by gathering client information or feedback in the areas of group selection and pre-group preparation, group process, and outcome. The Group Readiness Questionnaire (GRQ) is one measure that was created in the hopes that it could predict which potential group members would benefit from group psychotherapy. The GRQ was designed to capture a potential group member's expectations regarding the helpfulness of group therapy as well as positive and negative interpersonal skills that could affect process within the group. This study tests the ability of the GRQ to predict group process and outcome during the early, middle, and late stages of group while taking the interdependent nature of group data into account through multilevel analysis in an effort to establish the GRQ as a PBE measure. Clients who perceived themselves to be less inclined to participate actively in group settings felt less connected to their groups during the early stage of group, but began to feel more bonded to other group members during the middle stage of group. Group members who had lower expectations of group therapy being helpful to them initially felt less connected to their groups and perceived more conflict within their groups after the initial session. Group members who were less prepared in general for group therapy tended to feel more gradually connected to other group members during the middle stage of group. Group members who were less inclined to participate and self-disclose in group settings as well as ones who were overall less prepared for group tended to be experiencing greater initial distress before starting group therapy. Implications of these findings as well as directions for future research are discussed.