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Evaluation of Surrogacy for Survival and Binary EndpointsWe use the colorectal cancer study to illustrate the analysis for the survivalbinary surrogacy setting using the informationtheoretic approach. The true endpoint is overall survival and the surrogate endpoint is a twocategory tumor response: patients with complete or partial response are considered as responders and patients with stable or progressive disease are considered nonresponders. The data structure for the survivalbinary setting is shown in Section 12.5. The SAS Macro %SURVBININFOThe informationtheoretic approach discussed above can be used to evaluate surrogacy in different settings. In this section, we present the results for the survivalbinary setting using the SAS macro %SURVBININFO. The macro fits logistic regression and the Cox proportional hazards model for a binary and survival endpoint, respectively, and uses the models formulated in (12.53) to estimate triallevel surrogacy: %SURVBININFO(data=colo,true=Surv,trueind=survind, surrog=responder,treat=treat,trial=center, patid=patientid,weighted=1, model="reduced",boot=10) Arguments specific to the %SURVBININFO are: • model: the model used in (12.52) and (12.53) ("Reduced" or "Full"). FIGURE 12.51 Trialspecific likelihood reduction factor (horizontal line: the overall LRF). TABLE 12.3 SAS macros available for analyses using the informationtheoretic approach.
FIGURE 12.52 The estimated likelihood reduction factor. Individuallevel and triallevel surrogacy measures with 95% C.I. FIGURE 12.53 The Colorectal Cancer Study. Trialspecific and overall LRF (horizontal line). sures are equal to i?h = 0.0797 (0.0561, 0.1033), and = 0.3559 (0.1096, 0.6216), respectively. Both surrogacy measures indicate that the binary tumor response is a poor surrogate for the overall survival. As a sensitivity analysis, trialspecific LRF is presented in Figure 12.53. Other Surrogacy SettingsSAS macros that were developed for the evaluation of surrogacy using the informationtheoretic approach are presented in Table 12.3. Note that, as discussed in previous sections in the chapter, the data structure depends on the surrogacy setting. 
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