Ultimately, association implies causation if all possibilities for spurious associations have been eliminated.” It is only because of “the difficulties of establishing true causality in the social sciences” that “the term association rather than causation is emphasized . . .” (Kandel, 2002a, p. 4). Causality is, however, readily refuted by the frequently observed “atypical” sequencing (see below) as well as the lack of “true association”. Even if present, association does not need to be spurious to be non-causal. A common “cause”, source of variance in the risk, may be a plausible explanation of sequential use, particularly when one drug is more available than another.
