In robustness analysis, hypotheses are supported to the extent that a result proves robust, and a result is robust to the extent that we detect it in diverse ways. But what precise sense of diversity is at work here? In this paper, I show that the formal explications of evidential diversity most often appealed to in work on robustnesswhich all draw in one way or another on probabilistic independence -fail to shed light on the notion of diversity relevant to robustness analysis. I close by briefly outlining a promising alternative approach inspired by Horwich's (1982) eliminative account of evidential diversity.
Robustness Analysis in ScienceTo verify that results are not simply artifacts of the particular means used to detect them, scientists often attempt to duplicate those results using other, diverse means. To the extent that a result is detected via numerous, diverse means, it is said to be robust. Robustness analysis (henceforth, "RA") is a mode of reasoning in which one supports a hypothesis via an analysis of the conditions under which a result is robust.Examples of RA from scientific practice abound. Famously, biologist Richard Levins (1966) proposes RA as a general means for deciphering, when using simplified models to study complex systems, whether a result "depends on the essentials of a model or on the details of the simplifying assumptions:"[W]e attempt to treat the same problem with several alternative models each with different simplifications but with a common biological assumption. Then, if these models, despite their different assumptions, lead to similar results we have what we can call a robust theorem which is relatively free of the details of the model. Hence our truth is the intersection of independent lies.