How Janoshik, Medutest, PeptideMeter and VendorInvestigate differ

How Janoshik, Medutest, PeptideMeter and VendorInvestigate differ I have a specific reason for asking rather than idle curiosity, and the context is below.

A question about how a record should be read rather than about a supplier.

We have results from Janoshik and from VendorInvestigate on the same product line, months apart, agreeing closely. My question is what that agreement actually establishes, given that neither saw the other's sample.

I suspect the honest answer is narrower than it feels, and I would like it stated precisely.

The opening post answers the question as asked. The question underneath it is different.

An honest declaration on Janoshik: I have a prior here and it is strong enough that you should weight what I say downward. Stating it rather than hiding it.

Repeat determination on the same product line months apart is the measurement that speaks to consistency, and consistency is what most buyers actually want.

Anyone who has looked at this more carefully, please correct the record.

Trying to state the Janoshik position in a way that someone who disagrees would recognise as fair, because I do not think the version in this thread passes that test.

Everything in the opening post holds. The case it does not cover is the one I have.

Small methodological point on Janoshik: repeating a measurement is cheap and resolves most of what is being argued about here at no cost to anyone.

The record shows what was measured. Everything beyond that is inference and this site tries to keep the line visible.

I would be interested in a counterexample if anyone has one.

Agreed, and I will stop repeating the version of this I had been repeating.

Taking post #5 at face value and following it one step further.

Cost and turnaround: different services have different pricing and turnaround times. Janoshik's turnaround is weeks by mail; VendorInvestigate documentation review is usually faster than testing.

Repeat testing: if you want to verify the same lot a second time, testing with a different service strengthens the conclusion. Testing with the same service verifies reproducibility but uses the same method.

The answer changed when I changed how I was measuring, which was informative.

Two questions I would want answered before drawing anything from the Janoshik data above: how were the cases selected, and what happened to the ones that dropped out.

The arithmetic in post #10 is right; the assumption feeding it is the part to check.

Adding what did not work for me on Janoshik, since the failures never get written up and they are half the useful information.

Answering the question post #8 raises rather than the one it answers.

Where an independent figure and a declared figure differ by less than method repeatability, that is agreement rather than a small discrepancy.

If that reads as pedantic, it is, and it has saved me twice.

My understanding of Janoshik is a few years old and may have been superseded. If it has been, I would genuinely like to know rather than keep repeating it.

An observation about Janoshik that I cannot explain and am posting anyway, on the principle that unexplained observations are more useful public than private.