Spectrum of Possible Comparisons (1 of 3)  Alternative treatments  Most common scenario and typically least biased  More clinically meaningful and methodologically valid  Could still result in confounding by severity if not adequately controlled through design/analysis  No treatment/testing  Absence of exposure or absence of exposure and use of an unrelated treatment (active comparator)  Choice of time 0 must be clinically appropriate in order to reduce bias
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