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Acute Pain | Chronic Pain | General

What does "evidence" mean in chronic pain


Clinical bottom line

As well as well understood biases, new forms of bias or potential bias in chronic pain studies are emerging. Unless we take care, we can make the wrong decisions when comparing therapy efficacy unless like is compared with like, and at the highest level of evidence.

Moore et al. "Evidence" in chronic pain--establishing best practice in the reporting of systematic reviews. Pain 2010 150: 386-389.

Starting point

We know that there are limitations in evidence, and that higher quality studies produce, almost overwhelmingly, more conservative results than those with less rigorous methods. Understanding exactly what quality, or validity, means, is a dynamic, and we have to keep relearning lessons and ratcheting up the minimum standards we accept for "evidence". This review casts a cold and fishy eye over evidence in chronic pain trials.


The review makes the following points about what constitutes good evidence:

Core outcomes

It seems likely that future systematic reviews, and trial analysis, will be based on some core outcomes of benefit and harm. A likely set of outcomes for chronic pain is likely to include some or most of the following:

Making comparisons

Indirect comparisons between treatments can be made where there is an adequate amount of good quality data. Comparability is imperilled when like is not compared with like - when, for example, results from small, short studies with easily-attained but inadequate outcomes are compared with large, long duration studies with clinically relevant outcomes that are hard to attain. It is also imperilled when different doses or treatments are erroneously combined under a general label and then discussed as identical. Meaningful comparison of efficacy with other interventions is not possible where quality, validity, and size standards are not met by any one of the comparators.

Yet making comparisons between treatments is what we try to do all the time, in making decisions about individual patients, when making policy, and making guidelines. The bottom line is that we will have to be much more careful in future.