The Temporal Correspondence Limitation of Evidence-Based Policy Making: A Preliminary Discussion Towards an Astrophysics-Inspired State-Aware Epistemology of Governance

Evidence-based policy making assesses evidence for its reliability, for the credibility of its causal identification, and for its transportability to a target population. This paper identifies a further requirement that the established apparatus of assessment leaves unstated: the system state that a body of evidence represents must correspond to the system state obtaining at the moment of decision. Evidence is generated from a system at one time and intervention acts on that system at a later time, so a body of evidence may be reliable, well identified and appropriately transported, and still describe a condition the system has left. The requirement is called temporal correspondence, and it is distinguished from the classical problem of induction: granting the uniformity of nature leaves it in force, since a stable law applied to a superseded state yields a decision addressed to no existing condition. The paper develops the requirement by comparison with astrophysics, an observational science whose object is accessible only through signals that departed it in the past, and which has accordingly built its epistemology on the assumption that observation is historical. Fifteen elements of that discipline's practice are examined in turn and tested for transfer to governance, in three families: the reconstruction of a past state from a present signal, the constraints imposed by the observing situation, and the self-discipline of the observing community. The pattern of what fails to transfer is treated as the object of the enquiry, on the ground that it characterises governance as an observational situation. Six contributions are claimed. The paper states the requirement and establishes its independence from the problem of induction. It shows by inspection of the instruments, in place of inference from their consequences, that the dominant apparatus of evidence assessment contains no corresponding category, and it accounts for the omission. It classifies the ways in which the practices of a mature observational science fail to transfer, and it identifies the limit beyond which the comparison supplies nothing. It derives a set of requirements on the handling of evidence, each of which costs discipline in place of apparatus. And it allocates the burden of justification where the requirement fails and a course would be irreversible. The inspiration the comparison affords is accordingly a discipline of observation and report, and no technique for recovering the present condition of a governed system from lagged observation of it.