Why Folklore Secondary Lists Are Dangerous

Mostly from each other. A forum post becomes a blog post, the blog post becomes a downloadable checklist, and the checklist becomes the source for the next forum post. Somewhere near the start there was usually one person's genuine experience, which is not nothing. It is just not evidence about anybody else.

Very little of this is dishonest. Copying is what people do with information that is hard to check, and medical literature is hard to check if nobody has shown you how. The result is a body of confident material with no citations in it, which then gets treated as settled because it is everywhere.

There is a commercial layer on top of that, and it is worth naming as a structure rather than as a story about villains. Businesses that charge for help with claims have an interest in long lists of possible conditions, because a long list makes the problem look complicated enough to need buying help with. That incentive shapes what gets published without anybody having to lie.

Plantar fasciitis is the clearest case in the whole subject.

The claim, repeated constantly, is that heel pain changes the way a person walks, and that the altered gait wears out the knees, then the hips, then the low back. It has the shape of an explanation. It follows the body upward in a sensible order. Anyone who has limped for a week finds it easy to believe.

Here is what the literature says. Searching PubMed for plantar fasciitis secondary knee pain gait alteration cohort returns no results. Searching for plantar heel pain altered gait proximal joint osteoarthritis risk returns no results. Not weak results. None. Both searches were run on 21 August 2026 and either can be run again in under a minute.

Meanwhile there is real literature on plantar fasciitis, and it points somewhere else. A systematic review of 51 studies looking at 104 possible factors found one clear clinical association, a higher body mass index, and consistent imaging findings in the heel itself. The authors then write that there is a lack of evidence for the dogma of clinical and mechanical measures of foot and ankle function (PMID 26644427). The mechanical story the entire chain depends on is the specific thing the evidence does not support.

This one is harder to spot, because the pattern is genuine.

Take the most repeated claim in this category: a bad knee makes you favor the other leg, and the other knee wears out. The pattern is real. Of 117 people followed after having one knee replaced, about 37 percent had the other knee replaced within ten years.

But the same study looked at what predicted it. The strongest predictor by a distance was how much arthritis the other knee already showed on its own X-ray before the first operation. Age, sex, body mass index and which side had been operated on were not predictors at all (PMID 12913941).

So the second knee often does follow. What that study found driving it was the second knee's own condition, not the surgery on the first.

The prediction is right. The explanation welded onto it is not the one the evidence supports. A list that prints the pattern with the limping story attached has taught somebody something false while appearing to be correct, which is the hardest kind of error to catch.

The same failure runs the other way with tinnitus and hearing loss, which almost everyone treats as one thing. A study comparing the genetics of 596,905 people in the Million Veteran Program concluded that tinnitus is a distinct disorder separate from hearing difficulties (PMID 38242899). They appear together because inner ear damage often produces both.

Researchers hedge on purpose. The hedge is where they tell you how far the finding travels. It is also the first thing removed when a study becomes a bullet point.

The best known study linking sleep apnea to high blood pressure followed people for four years and found more apnea went with more hypertension. Its conclusion says the findings suggest sleep-disordered breathing is likely to be a risk factor (PMID 10805822). Suggest, and likely. By the time that reaches a checklist it reads as sleep apnea causes high blood pressure, which is a claim the authors declined to make with their own data in front of them.

Sometimes what gets deleted is a disagreement inside the paper. A review of sleep apnea and depression found no convincing association when it pooled cross-sectional studies and a doubled risk when it pooled studies that followed people forward (PMID 33158487). One line on a list cannot hold both, so one of them is dropped, and it is never the one that makes the list look shorter.

And sometimes what gets deleted is who the finding applied to. In nearly 10,000 Vietnam era veterans, PTSD went with high blood pressure in the men and did not in the women (PMID 40353294).

A pooled analysis of head injury and dementia did something similar. It found no extra risk from being a veteran. It also found that about twice as much dementia traces back to head injury among veterans, purely because so many more of them have had one (PMID 36305374).

Both papers say two things. Lists have room for one.

The most careful example is also the most quietly useful. A systematic review of 43 studies of PTSD and sexual difficulties found clear associations with desire, satisfaction and distress, and reported the results for erectile dysfunction specifically as mixed (PMID 34257051). That is one of the most confidently repeated pairings anywhere in this subject, and the review covering it is not confident.

Three things, and the first one is the one people underestimate.

It costs credibility in the room where it matters. Walking into an appointment with a printed list of conditions to be tested for changes the conversation, and not in the direction anybody wants. Clinicians recognize forum material quickly. The version of that appointment where somebody describes a symptom in their own words and the version where they present a checklist do not go the same way, and the symptom version goes better.

It aims attention at the wrong thing. Time in an appointment is short. Spending it on a pairing with nothing behind it is time not spent on the symptom that was actually worth examining.

And it makes people easier to sell to. A person carrying a long list of conditions they might have is a person who has been given a reason to feel the problem is too complicated to handle alone. Some of what is sold on the back of that feeling costs thousands and does nothing that a free accredited representative would not have done.

In about five minutes, with no subscription and no training. This is the part worth keeping.

Go to pubmed.ncbi.nlm.nih.gov. Type the two conditions in plain words with the word meta-analysis after them: sleep apnea depression meta-analysis. Nothing fancy. The search box handles ordinary language.

If nothing relevant comes back, try once more with different words. If two honest attempts return nothing, that is your answer, and it is a real answer rather than a failure to find one. It means nobody has published the finding, which means anybody asserting it is asserting it without support.

If something does come back, open it and read the abstract for four things. What kind of study is it, and does it say meta-analysis or systematic review anywhere. How many people or how many studies. What verb the authors use in the conclusion, because associated with and is a risk factor for are different claims and they chose between them deliberately. And whether the abstract contains a but or a however, because that sentence is usually the most informative one in the whole paper.

That is the entire method. It is also what the tool on this site does.

The tool prints the study type, the number of people and the authors' own sentence next to every entry. That is deliberate. It means any of it can be checked without taking our word for it, which is the only sensible way to read anything on this subject, including this page.

Start from the body rather than from the list.

If something has changed, describe the change to a treating provider as a symptom, in ordinary words, without a diagnosis attached. Numbness that started in the toes. Waking with headaches. Getting winded on a flight of stairs that used to be nothing. That gets examined. What gets examined gets written down.

A record built that way is worth more than any list, because it describes one person rather than a population, and because it has dates on it.

For the paperwork, a free VSO is accredited and does not charge. That is the honest first stop and it stays the honest first stop no matter what anybody is selling.