“Absence of evidence isn’t evidence of absence” is a slogan that is popular among scientists and nonscientists alike. This article assesses its truth by using a probabilistic tool, the Law of Likelihood. Qualitative questions (“Is E evidence about H ?”) and quantitative questions (“How much evidence does E provide about H ?”) are both considered. The article discusses the example of fossil intermediates. If finding a fossil that is phenotypically intermediate between two extant species provides evidence that those species have (...) a common ancestor, does failing to find such a fossil constitute evidence that there was no common ancestor? Or should the failure merely be chalked up to the imperfection of the fossil record? The transitivity of the evidence relation in simple causal chains provides a broader context, which leads to discussion of the fine-tuning argument, the anthropic principle, and observation selection effects. (shrink)

Certain predictions are such that their accuracy can be affected by their dissemination, by their being believed and acted upon. Examples of such reflexive predictions are presented. Various approaches to the precise delineation of this category of predictions are explored, and a definition is proposed and defended. Next it is asked whether the possible reflexivity of predictions creates a serious methodological problem for the social sciences. A distinction between causal and logical reflexivity helps support a negative answer. Finally, we consider (...) the thesis that "this characteristic of predictions is peculiar to human affairs" (Merton), and an attempted rebuttal (Grunbaum). It is argued that Grunbaum's rebuttal is ineffective. (shrink)

Professor Buck has given an illuminating account of the logical status of reflexive predictions in the social sciences. He tells us that the classification of a prediction as reflexive is predicated on a tacit distinction between the “normal” and the “abnormal” or perturbed conditions under which it is made. This seems to me to be a perceptive and sound circumscription of the class of reflexive predictions as encountered in the social sciences. He goes on to show helpfully how the social (...) scientist can cope with the pitfalls of spurious disconfirmation and spurious confirmation which are created by “self-frustrating” and “self-fulfilling” predictions respectively. And Professor Buck then offers some searching doubts concerning the adequacy of regarding self-fulfilling predictions as the pattern of racial discrimination against minority groups. Finally, he presents objections to my critique of Robert Merton's claim that self-defeating and self-fulfilling predictions are endemic to the domain of human affairs and are “not found among predictions about the world of nature.”. (shrink)