"Participants were recruited from general practices" — so none of the more serious cases, who would be under hospital clinic care.
"excluded participants with previously raised levels of serum alanine aminotransferase (≥3 times the upper limit of normal), with persistent, generalised, unexplained muscle pain (whether or not associated with the use of statins) and levels of creatine kinase five times or more the upper limit of normal" — so this study excludes some people who stopped or were stopping statins because of unexplained muscle pain, or because of two possible explanations for muscle pain?
"A common criticism of large placebo controlled trials of statins is that patients most likely to experience side effects are not included" — and yet, despite stating that, they do not directly address the above exclusions.
I would probably not have been recruited in the first place (due to being under hospital care not GP) but would have been excluded anyway by the report of unexplained muscle pain and one of my CK test results.
There also seems to be no attempt to measure and control for physical activity. My problems manifested themselves more when I tried to do more (at least my two worst episodes came while cycling uphill) and my reading suggests that this isn't unusual. It's a pretty powerful discourager, too, so if you are fearing muscle pain, maybe you do less?
Due to the above limitations, I'm not sure this tells us much useful about people who report severe muscle pain while taking statins. It is disappointing that the above design choices were not challenged before deployment.
The linked opinion is pretty insulting IMO, implying many reports are due to the "nocebo effect". It certainly wasn't for me. I expected statins to work. My father took Zocor for years without much obvious trouble. My doctors expected statins to work and I think most of them disregarded the side-effects, so it took years for my deteriorating mind and body to be linked to statins. Even then, I was very sceptical and kept a notebook of statin usage and muscle pain attacks primarily hoping to show the well-established statins were not the cause and I could continue taking them! Because since then, I've been on a treatment rollercoaster...
What I can't tell you is how common statin muscle problems are. Some of my relatives have suffered side-effects, even some who didn't know my troubles before, but I suspect that is understandable, as there are some genetic markers even flagged up as likely statin intolerance in some commercial DNA tests now.
I don't think a stream of selective-participant studies really help us work out the size of this problem, either!