The probability (p) value is a statistical tool that increases the confidence that an antibody has been identified with a scientifically acceptable level of uncertainty (0.05).
As applied to antibody identification, it is computed using Fisher's exact test. Trivia tidbit: This is the same Fisher who helped develop the Fisher-Race theory of Rh inheritance.
The p value is calculated using the number of cells that are positive and negative with the patient's plasma.
Calculating p values is beyond the scope of this case study. However, the attached PDF provides a basic overview of p value, its relationship to antibody identification in general, and its application in this Case Study.