The McNemar test is a test on a 2x2 classification table when you want to test the difference between paired proportions. Chi-square test for 2X2 tables compares the tallies or counts of categorical responses between two (or more) independent group
A discordant pair is a matched pair in which the outcomes differ from the members of the pair whereas concordant pair is a matched pair in which the outcome is same for each member of the pair.
McNemar's test uses only the number of discordant pairs, that is, the number of pairs for which the control was exposed to the risk factor.
Provide an example of when a discordant pair test is employed? Looking at relationships of variables is common in research, in fact there is much comparing similarities and differences. Elaborate on this.