Quantile treatment effect of zinc lozenges on common cold duration: a novel approach

What is it about?

Previous meta-analyses have indicated that properly composed zinc lozenges can shorten common cold duration, while negative findings can be largely explained by shortcomings in the composition of lozenges or in the study protocols. The size of the effect of zinc lozenges should be considered in the context of practical significance. An average effect such as the 4-day reduction in cold duration in the Mossad (1996) trial might hide substantial variation in the treatment effect. In our study, we used the quantile treatment effect (QTE) approach and found that in the Mossad study zinc lozenges shortened 15-17-day colds by 8 days, but 2-day colds by just 1 day.

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Photo by Brittany Colette on Unsplash

Photo by Brittany Colette on Unsplash

Why is it important?

Sample size calculations for RCTs are usually based on an assumed uniform effect over the participant population. Thereby the analysis of observations is also based on the assumption of a uniform effect, and most medical literature on treatment effects is focused on the average effects. However, biology is complex and a single average effect may not apply over all participant subpopulations. The QTE-approach allows separate analyses of effects on short and long durations of illness. In clinical medicine, there is usually a greater interest in the effect of a treatment on long illness duration than on short illness, and the QTE-approach yields information on such effects. The 8-day reduction in common cold duration for those with expected 15-17-day colds in the Mossad trial is a much more clinically important finding than the 1-day reduction for 2-day colds. Such variation in the treatment effect is masked in the calculation of the overall average effect of 4 days.

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