Table 3. Six possible scenarios when the numbers of the exposed and unexposed groups are balanced.^a.

	Actually exposed	Actually unexposed
Scenario #1
Subject ID	#1, #2	#3, #4
Response type	doomed, preventive	immune, preventive
Scenario #2b
Subject ID	#1, #3	#2, #4
Response type	doomed, immune	preventive, preventive
Scenario #3
Subject ID	#1, #4	#2, #3
Response type	doomed, preventive	preventive, immune
Scenario #4
Subject ID	#2, #3	#1, #4
Response type	preventive, immune	doomed, preventive
Scenario #5
Subject ID	#2, #4	#1, #3
Response type	preventive, preventive	doomed, immune
Scenario #6
Subject ID	#3, #4	#1, #2
Response type	immune, preventive	doomed, preventive

^aScenarios #1 and #3 are identical from the perspective of counterfactual reasoning, because the distributions of response types are the same in these scenarios. Similarly, scenarios #4 and #6 are identical from the perspective of counterfactual reasoning. Consequently, these six scenarios are grouped into a total of four patterns in terms of the distributions of response types.

^bExposure status shown in Table 1 corresponds to scenario #2.