Ultrasound and skinfolds: operator dependence in practice — setting out what I have, and where I think it stops being reliable.
Trying to establish the boundary conditions on ultrasound and skinfolds. The general claim is fine; I want to know where it stops holding, because that is where I am operating.
Three edge cases below, in increasing order of how far outside the usual range they sit.
Narrowing the opening post, because the general version has more than one answer.
Ultrasound: thickness of subcutaneous fat at specific sites. Less standardised than DXA and operator-dependent. Useful as a supplementary measure but not as a primary method.
Ultrasound and skinfolds is worth one more sentence than it usually gets, and the sentence is the one about how the number was arrived at.
An honest declaration on ultrasound and skinfolds: I have a prior here and it is strong enough that you should weight what I say downward. Stating it rather than hiding it.
Where I part company with post #3, and it is a narrow parting.
Distinguishing three things in the ultrasound and skinfolds discussion that keep getting used interchangeably: the observation, the proposed mechanism, and the recommendation that gets attached to both.
The most useful protocol is the one you will actually repeat identically. An imperfect measurement repeated consistently beats a better one repeated carelessly.
On reflection I would soften that slightly.
I would keep ultrasound and skinfolds and the decision it usually gets used for separate in this thread. They are related and they are not the same question, and merging them is why the last one went badly.
Answering the question post #10 raises rather than the one it answers.
Photographs under fixed lighting and posture are a genuine record and are the hardest of these to standardise.
Two things can be true about ultrasound and skinfolds at once: the mechanism is plausible and the evidence for the size of the effect is thin. Most of the argument here is people defending the first against attacks on the second.
Before the thread moves on from ultrasound and skinfolds — what is the sample size behind the claim? I am not being difficult; I have seen the same figure quoted from an n of four and from an n of four hundred.
Post #14 describes the usual case. This is about the unusual one.
I keep a log for ultrasound and skinfolds specifically because my memory of it turned out to be systematically wrong in one direction. Six weeks of notes cost nothing and settled it.
I had written a reply contradicting post #18 and deleted it. Here is what survived.
Ultrasound: thickness of subcutaneous fat at specific sites. Less standardised than DXA and operator-dependent. Useful as a supplementary measure but not as a primary method.
Taking post #19 at face value and following it one step further.
Reporting rather than recommending, on ultrasound and skinfolds. What happened is above. Whether it should have is a different question and not one I am qualified to answer.
On ultrasound and skinfolds I would separate what is worth knowing from what is worth acting on. The first list is long and the second is short, and conflating them is how threads get heated.
Post #23 put the caveat in the right place and I want to underline it.
A note on how ultrasound and skinfolds gets discussed rather than on ultrasound and skinfolds itself: the confident posts get the replies and the careful ones get ignored, and the careful ones have been right more often.
Ultrasound and skinfolds came up in a thread eighteen months ago and was answered well. I cannot find it, which is itself the problem, so here is the reconstruction.
Neither method is capable of detecting the month-to-month changes that people report detecting month to month.
That is all I can say without guessing.
Where I would push back on the ultrasound and skinfolds consensus is the confidence, not the direction. The direction looks right. The confidence is borrowed.
Picking up post #27: that is the part I would want checked first.
Small methodological point on ultrasound and skinfolds: repeating a measurement is cheap and resolves most of what is being argued about here at no cost to anyone.