Causal inference, mechanisms, and the Semmelweis case

Abstract

Semmelweis's discovery of the cause of puerperal fever around the middle of the 19th century counts among the paradigm cases of scientific discovery. For several decades, philosophers of science have used the episode to illustrate, appraise and compare views of proper scientific methodology.Here I argue that the episode can be profitably reexamined in light of two cognate notions: causal reasoning and mechanisms. Semmelweis used several causal reasoning strategies both to support his own and to reject competing hypotheses. However, these strategies have gone unappreciated in the existing literature. I show that a causal reasoning approach makes sense of the multitude of tables in Semmelweis's main text, which in later editions were often abridged because they appeared redundant.Moreoever, the existing literature tends to focus on Semmelweis's clinical intervention and on the extent to which it alone confirms his theoretical conclusions. This neglects Semmelweis's efforts to show by animal experiments that his clinical results are in agreement with a demonstrable mechanism of puerperal fever pathogenesis. I argue that the full evidential force of Semmelweis's argument can only be appreciated if both his clinical and his laboratory investigations are taken into account.

Spot the difference: Causal contrasts in scientific diagrams

“…We find that many common forms of graphical representation originated or developed in the 19th century, but they were slow to gain acceptance (Funkhouser, 1937;Friendly, 2008). Less than a century before Doll and Hill, Ignaz Semmelweis's Etiology of Childbed Fever (1861) presented its findings on differences and trends in mortality rates exclusively in tabular form, despite their suitability for graphical representation (Scholl, 2013). Bechtel and Abrahamsen (2015) cite Wunderlich's (1868) pioneering work on daily oscillations in body temperature as another instance of the 19th century preference for tables.…”

The Material Theory of Induction

“…The brief remarks above already indicate how well Semmelweis' methodology is captured by Mill's methods. Scholl (2013) has given a more thorough analysis of Semmelweis' methodology and finds extensive use of Mill's methods, including Mill's method of agreement and concomitant variation. Scholl (2015) argued for the failure of Lipton's attempts to impugn the understanding of Semmelweis' analysis as an application of Mill's methods.…”

The judgements that evidence‐based medicine adopts

“…We would risk repeating historical errors, in which relevant evidence was dismissed because at the time, there was no established causal mechanism that could make sense of it. As an example, in the much quoted case of Dr. Semmelweis, evidence that antiseptic routines reduce infections at childbirth was rejected as implausible because there was no accepted understanding of how this could happen …”