Ganesh, IIMs shortlist candidates for the interview stage based on their own criteria, which may be independent of each other. The process may include Written Ability Test, Group Discussion, and Personal Interviews. Performance in the CAT examination is an important component in the admission process. IIMs may additionally use other factors such as the previous academic performance of the candidates, relevant work experience, gender and academic diversity and other similar inputs in shortlisting and ranking of candidates at various stages of the admission process. The processes, academic cut-offs and the weights allocated to the evaluation parameters may vary across IIMs. So by poor if you mean just pass or below average, even if you score 98 percentile in CAT, it becomes difficult to be shortlisted by IIMs. Because there is a rating scale for the Academic section and a final composite score is calculated.