Where a manufacturer was involved, the reported effect was far bigger
Fifteen glucosamine trials disagreed sharply. With no manufacturer involved, effect sizes ran 0.05 to 0.16; with one, 0.47 to 0.55. Patients and trial length did not explain it.
What the study found
Manufacturer-involved glucosamine trials reported far larger effects
Fifteen glucosamine trials disagreed sharply, and what separated them was not the patients or the length of the trial. Where no manufacturer was involved, effect sizes ran 0.05 to 0.16. Where one was, 0.47 to 0.55. An analysis of the ten largest trials found the same split.
The caveat · Funder, salt and rigour go together
Manufacturer involvement, the salt used and whether allocation was concealed are almost perfectly entangled here, so this cannot say which explains the gap. These are comparisons across trials, not a randomised contrast, so sponsorship is associated with the result, not shown to cause it.