What is a Cause and How Do We Know One? A Grammar for Pragmatic Epidemiology

Abstract

In this paper, criteria used by many epidemiologists as aids in causal inference are reviewed and revised. The revised scheme emphasizes the distinction between essential properties of a cause and criteria useful for deciding on the presence of these properties in a given case. A systematic procedure for causal inference tests each essential causal property in turn against appropriate criteria. For a pragmatic epidemiology in which all determinants serve as causes, their essential properties are held to be association, time order, and direction, in an ascending hierarchy. Criteria for association are probabilistic and can be enhanced by strength and consistency. Given association, criteria for time order of the relevant variables follow from access to observation, which is dependent on design. Given association and time order, causal direction (or consequential change) calls on an array of criteria, namely, consistency and survivability, strength, specificity in cause and in effect, predictive performance, and coherence in all its forms (e.g., theoretical, factual, biologic, and statistical). The evolution of such criteria is traced through the epidemiologic literature in the light of historical context. Although Popper's philosophy cannot directly serve an inherently inductive judgmental process, his notion of survivability has here been added, alongside replicability, as a subclass of consistency. This criterion is proposed to bridge the gap between the particularity of designs and the generality required of causal relations. Designs are ordered and described in the framework of testing survivability. Finally, definitions are offered for the list of criteria deployed.

Demonstrating Nutrient Cost Gradients: A Brooklyn Case Study

“…As shown in Tables I and II, there are low cost items in each domain that could be used to achieve this goal. While the USDA meal plans are designed to provide the macro-and micro-nutrients necessary in the diet to prevent malnutrition [12,13,40,44], questions remain as to the adequacy of micronutrient intake when energy intake is limited to recommended levels [10,12].…”

“…Associations taken alone, however, are insuffi cient to show a cause and effect relationship between food costs and actual micronutrient defi cient diets [10 -13]. "For a pragmatic epidemiology in which all determinants serve as causes," writes Merwyn Susser, "their essential properties are held to be association, time order, and direction in an ascending hierarchy [13]." Susser's criteria have not been met for the income to defi ciency paradigm, since there are inconsistencies in both associations between low-income and malnutrition and in the sequence of low-income and food selection narratives [10 -12].…”

Looking Back on “Causal Thinking in the Health Sciences”

“…criterion in 1986 (54), and the most general consideration in the strategy of simplifying conditions of observation (i.e. a hierarchical classification of basic structures of study design) was moved to one part of a bifurcated consistency criterion in 1991 (57). Nevertheless, the many important considerations of study design and implementation that remain, as well as the strategies of screening for confounders and elaborating associations in their entirety, survive as crucial elements of Susser's approach to causal inference that are not (yet) subsumed by the list of causal criteria.…”

“…How, in light of a criterion that nonlinear or nonmonotonic dose-response curves neither affirm causality nor detract from it (54)(55)(56)(57), are we to interpret observations of large numbers of epidemiologists who, themselves, interpret such curves as evidence against causality? Do these observations count as evidence against the ?…”

“…Susser's discussion of causal criteria occupies only a brief 22 pages in the original text, but it helped spur a vigorous discussion of the use of such criteria, which has persisted unabated to the present day, including substantial refinements by Susser himself (52,56,57). Although the basic outline of the modern set of criteria has evolved little since formulation by a Surgeon General's Advisory Committee (60) and Hill (15), their philosophical justification, relative merits, and specific interpretation have been the subject of continued and sometimes contentious debate.…”