ASH two choices model vs a 3-choices decision model. (A) ASH modeling approach for determining the effect of thrombophilia testing. The model starts with the population considered for thrombophilia testing. Thrombophilia testing refers to testing for any type of thrombophilia or a specific type. Intervention is the course of action other than usual care. Depending on the particular question, this means prescribing thromboprophylaxis, withholding thromboprophylaxis, extending thromboprophylaxis, stopping thromboprophylaxis, withholding birth control pills, or withholding hormone replacement therapy. Usual care typically consists of short-term (3-6 months) anticoagulation (provoked VTE) or indefinite treatment (unprovoked VTE). P-thrombophilia prevalence (denoted in the manuscript as T_p); incidence risks of VTE recurrence is denoted in the manuscript as p_t+ and p_t- for patients with (thrombophilia) positive results and for patients with negative test results, respectively; Association refers to RR for recurrent VTE in patients with thrombophilia vs patients without thrombophilia (RR_t); Relative effects of intervention (anticoagulant) on VTE recurrence (RR_rx) and bleeding (RR_bleed) compared with no intervention. (B) A decision tree showing a 3-choice clinical dilemma: administer treatment (anticoagulants) vs performing a diagnostic test (T) (thrombophilia testing) vs withholding therapy. Each treatment consists of the management strategies “treat all patients,” “treat none,” and “use thrombophilia test” to decide whether to treat. By “treatment,” we refer to a commitment to a course of action that may include management consisting of treatment or diagnostic testing. p_t+=Pr(D+|T+) refers to the probability of VTE recurrence when the thrombophilia test is positive (T+). U1 to U4, utilities (outcomes; see Appendix 1 for details).