Sufficiently Important Difference for Common Cold

Severity Reduction

This paper defines the term "sufficiently important difference" (SID), a concept that has grown in importance with the rise in evidence-based medicine. SID is the "smallest amount of patient-valued benefit that an intervention would require in order to justify associated costs, risks, and other harms." In particular, this research sought, through in-person and telephone interviews, to estimate the SID for treatment of the common cold. The authors tested four scenarios: treatment with vitamin C, echinacea, zinc lozenges and the unlicensed antiviral drug pleconaril. Scenarios were varied to determine at what level of illness reduction patients would accept the treatment, weighing various harms, costs, etc.

Data analysis focused on determining the amount of reduction of cold severity respondents required in order to say that they would take each treatment. Vitamin C was ranked as requiring the least benefit to justify treatment, then echinacea, then the zinc lozenge, and last the antiviral. Mean severity-reduction SID for the antiviral (57%) was more than twice that of the vitamin C scenario (25%). This means that patients required the antiviral to provide a mean 57 percent reduction in severity of their cold before they would take it, versus a 25 percent reduction in severity before they would take a vitamin C pill. A consistent finding between this study and other similar studies was the trimodal nature of the data: some people will take a treatment regardless of the benefit, some will not take a treatment regardless of the benefit, and most people require a certain amount of benefit to justify cost and risks.

The authors conclude that existing cold treatments do not provide the requisite SID desired by patients in this study. The benefit of current cold treatments is controversial at best, and certainly does not meet the 25–57 percent reduction in severity indicated by patients in this study as a requirement of taking the treatment. These results are particularly significant when applied to other medications with modest effect sizes. For example, evidence on the efficacy of antidepressants suggests that by taking an antidepressant a patient might expect a 1–2 point reduction in depression on the Hamilton Depression Rating Scale, out of a possible 20 points indicating the person is depressed. Given that antidepressants are relatively expensive and often have side effects, the authors pose the question, "if patients…were provided simple descriptions of likely benefits and harms, how many would choose these treatments?" The development of the SID concept as a benchmark is a crucial one in advancing medical decision-making for both patients and caregivers.

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