How much of treatment effect is needed to actually matter?
PainSci summary of Williams 2011?This page is one of thousands in the PainScience.com bibliography. It is not a general article: it is focussed on a single scientific paper, and it may provide only just enough context for the summary to make sense. Links to other papers and more general information are provided at the bottom of the page, as often as possible. ★★★☆☆?3-star ratings are for typical studies with no more (or less) than the usual common problems. Ratings are a highly subjective opinion, and subject to revision at any time. If you think this paper has been incorrectly rated, please let me know.
There are various ways of measuring improvement in scientific tests of treatments. As this paper points out, “when an outcome measure improves by, say, five points it is not immediately apparent what this means.” How much improvement matters? It is extremely common for experimenters to confirm real, statistically significant treatment effects that are nevertheless trivial. This paper discusses how much benefit is needed to be taken seriously, and cites the damning example of spinal manipulation. Chiropractors routinely claim that the benefits of spinal adjustment are “proven,” but the authors point out that trials have “shown an effect size for manipulation that is less than the threshold for what is clinically worthwhile.”
I think it’s particularly noteworthy that these authors have no particular axe to grind about chiropractic treatment — this is not a paper about that. They simply needed a good example to make their point, and it’s telling that they picked spinal manipulative therapy.
Patient-based outcome measures have been developed to measure the health status of patients suffering from many conditions found in musculoskeletal medicine. Many types have been developed. Generic measures can be used across a broad spectrum of illness and can compare the health of an affected group with that in the general population.1 Condition-specific instruments on the other hand measure the effect of a single condition on health. Compared to generic measures they have a narrower focus and are more sensitive to small but clinically significant changes in health status over short periods. Examples include the Roland–Morris questionnaire2 for low back pain and Western Ontario McMaster universities arthritis index (WOMAC) for osteoarthritis.
These two articles on PainScience.com cite Williams 2011 as a source: