Steady state trials another valid substitution of

Authors: Okujou Iwami Masayuki Ikeda

Publish Date: 2013/05

Volume: 18, Issue: 3, Pages: 237-

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Abstract

Many traditionally established medical interventions are not examined with randomized trials especially in emergency medicine We researched what is the scientific basis of the measurement of the causal effect in these interventions and proposed another trial to measure causal effectsWhen the state of the observed person is fairly steady before an exposure the ratio of the afterperiod to the beforeperiod of the exposure is sufficiently small and changes are obtained in relatively short time it is possible to postulate that the state of the counterfactual person to be compared is almost equal to the state of the real person before the exposure Bayesian approaches show that the causal effect of the exposure is estimated even in only oneperson steady state trials when large changes are observedSteady state trials are valid methods to measure causal effects and can measure causal effects even in oneperson trials When we can measure the causal effect of interventions with steady state trials these interventions should be regarded as scientific without use of randomized trialsEvidencebased medicine EBM appeared as a handy tool kit for clinicians who had not understood the basic thinking of epidemiology 1 After the advocates of EBM succeeded in nominating randomized trials to be paramount 2 the socalled “Hierarchy of Strength of Evidence” towered in medical practice and many clinical guidelines prostrated themselves in front of the pyramid 3 4 Many traditionally established medical interventions were stripped of their rank for reasons having to do with observational studies Under these circumstances Smith and Pell 5 asked a sarcastic question why protagonists of EBM did not participate in a randomized trial of parachute useIn epidemiological studies the counterfactual or potentialoutcome model has become increasingly standard for causal inference 6–8 However the theoretical ideal to measure causal effects of exposure is impossible To achieve a valid substitution for the counterfactual experience we resort to various design methods that promote comparability One approach is a crossover study and another is a randomized trial Other approaches might involve choosing unexposed study subjects who have the same or similar riskfactor profiles for disease as the exposed subjects 9 Casecrossover design was introduced for estimating a short term transient effect of intermittent exposures on acuteonset diseases 10 11 For each case one or more predisease or postdisease time periods are selected as matched control periods for the case The exposure status of the case at the time of the disease onset is compared with the distribution of exposure status for the same person in the control periods The key feature of the casecrossover design is that each case serves as its own control In this paper we expand this key feature and propose another valid substitution of the counterfactual ideal to measure causal effects and show that parachute use and many interventions in emergency medicine have the scientific basis of the causal inference without randomized trialsCounterfactual model We establish a hypothetical person in the counterfactual world in order to compare the outcome of the exposed person with the outcome of the unexposed person After the exposure both the conditions of the exposed person and the unexposed person are observed at the same time As the only difference between the two settings is the exposure it is possible to measure the effect of the exposure

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