Investigated whether the probability of using context-based information in forming a frequency judgment is inversely proportional to the diagnosticity of the alternate inputs accessible in memory, using an accessibility-diagnosticity framework. Exp 1 (n=151) showed that when memory-based information is accessible and diagnostic, contextual information is not used. Exp 2 (n=177) showed that when memory-based information is accessible but not diagnostic, the use of contextual information depends on its perceived diagnosticity. Exp 3 (n=80) showed that when memory-based information is not accessible, contextual information is used even when its diagnosticity is questionable. Implications for consumer research are considered. (PsycINFO Database Record (c) 2007 APA, all rights reserved)