Decision tables are used to model complex decision logic by considering different combinations of conditions and actions. Based on the given decision table for prescribing drug therapy:

Column 1 and Column 3 both result in the same actions (prescribing Amoxicillin).

These columns can be merged because the actions taken do not depend on whether the patient is taking anticoagulant therapy (both are 'T' for this condition).

Thus, combining these columns simplifies the decision table without losing any information.