The therapeutic outcomes model (TOM) provides a logical and consistent manner in which bacteriologic and clinical efficacy can be predicted and calculated. It not only allows antibiotics to be ranked in efficacy, it gives precise estimates of the magnitude of differences in efficacy, which is typically lacking in older antimicrobial guidelines. The TOM identifies the major variables that need to be considered in accurately estimating outcome and places those variables into the appropriate relationships and formulas so that outcomes will be automatically calculated. In the case of rhinosinusitis, the major variables are (1) likelihood of spontaneously resolving nonbacterial cause, (2) likelihood of nonresolving nonbacterial cause, (3) prevalence of subcauses (eg, different species of bacteria), (4) the spontaneous resolution rates of each subcause, (5) the antibacterial efficacy of the treatment (eg, antibiotic) against each of the subcauses, and (6) the compliance rate of the treatment recommended. Minor variables, such as prior antibiotic use, patient age, or bacterial vaccination status, affect the efficacy of a given agent by modifying the value of one or more of the major variables. The TOM is a superior mechanism for ranking and evaluating relative antibiotic efficacy than previous methodologies.