Both analgesia trials today are large, well conducted, and report statistically significant differences that no patient would notice. That is not a flaw in either trial. It is what happens when a study is powered to detect a difference smaller than the one that matters.
The numerical rating scale for pain has a well-established minimum clinically important difference of about 1.3 points. Below that, patients cannot reliably tell two states apart. The ketamine trial found 0.72 points with a tight interval; the magnesium trial found every timed difference under the threshold. Both authorship teams said so explicitly, which is good practice and still routinely lost when a result is summarised.
The habit: before reading a p value on a symptom scale, find the minimum important difference for that scale, and compare the confidence interval to it. If the whole interval sits below that threshold, the trial has shown a real difference that does not matter — a useful and quite different finding from no difference at all.
- Pain NRS: about 1.3 points is the smallest difference patients detect
- Compare the whole confidence interval to that threshold, not just the point estimate
- An entire interval below the threshold means real but imperceptible
- Large trials detect differences far below the ones worth acting on
- Check whether a binary success outcome is a threshold applied to the same scale
The statistics, in plain English
Statistical significance answers whether a difference is likely to be real; the minimum clinically important difference answers whether it is worth having. A large trial separates these completely, because power rises with sample size while the threshold of perception does not move. Reporting both, as both trials here did, is what lets a reader tell them apart.
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