Anti-Jk^{a}, anti-E, and anti-c have been confirmed but not all with an acceptable degree of probability (see below). The other possible antibodies have been excluded.

#### p Values

An easy way to calculate p values is to use the 3 pos/3 neg guideline, since this will produce a p value of 0.05:

- The patient did not react with 5 cells that are Jk(a-) E- c- (1 in the initial panel and 4 in the exclusion panel). The criterion of 3 negatives has been met by all 3 likely antibodies.
**Anti-Jk**The patient reacted with 4 cells that are Jk(a+) E- c- (3 in the initial panel and 1 in the exclusion panel).^{a}:**Anti-E:**The patient reacted with only 1 cell that is E+ Jk(a-) c- (1 in the exclusion panel).**Anti-c:**The patient reacted with 3 cells that are c+ Jk(a-) E- (2 in the initial panel and 1 in the exclusion panel).

Anti-Jk^{a} and anti-c have met the criterion of a p value of at least 0.05, indicating that there is only a 5% chance of getting the results due to another antibody (chance).

However, anti-E has not because the patient reacted with only 1 cell that is E+ but negative for the other 2 presumptive antibodies, anti-Jk^{a} and anti-c.

- To obtain the minimum acceptable p value for anti-E, 2 more cells that are E+ Jk(a-) c- would need to be tested and be positive.

#### Online p value calculator

See this online tool for calculating p values - Enter values as follows:

- Change
*Outcome 1*to*negative*and*Outcome 2*to*positive* - Change
*Group 1*to*antigen-neg (e.g., E-)*and*Group 2*to*antigen-pos (e.g., E+)* - The 2 x 2 table would look like this:
Negative Positive E- 5 0 E+ 0 1 - Choose Fisher's exact test
- Use a
**one tailed test -**A one-tail p value is appropriate only when previous data or common sense tell you that a difference, if any, can only go in one direction. Obviously, with antibody identification, we expect cells that are antigen-positive to react (and vice versa). - Hit the
*calculate*button

**Caution #1: **Statistical calculations do not substitute for carefully examining serologic test results. It is critical to consider p values as just another tool. If acceptable, they provide additional converging evidence to support the conclusion regarding which antibody has been identified.

**Caution #2: **With complex antibody combinations, some blood banks prefer a minimum p value of 0.01 as an added measure of probability.