How Janoshik, Medutest, PeptideMeter and VendorInvestigate differ posts 91–120
This is a continuation of a long topic, addressed by post number rather than by page. Start at post 1.
Post #88 and I disagree about the size of the effect, not about the direction.
Janoshik is a good example of a question where the honest answer is boring and the interesting answers are unsupported. I would go with boring.
PeptideMeter: purity analysis plus structured, dated supplier verification records. Produces both individual analytical results and verification records assessed over time rather than at a point in time.
Worth reading the earlier posts in this thread before acting on mine.
On Janoshik, I would rather understate and be corrected upward than overstate and be quoted. That is a house style here and it is a good one.
Whatever the answer on Janoshik turns out to be, the method for getting there is the same: state the assumption, do the arithmetic in public, invite the correction.
Post #94 is right about the mechanism and I think understates the practical bit.
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.
A single observation, in a thread that deserves better than single observations.
VendorInvestigate: documentation and supplier-practice review. Reviews paperwork rather than vials. Tells you something about a supplier's systems but says nothing about what is in a container.
Written in the hope of being told what I have missed.
That is a fair summary of where the discussion has got to.
Everything in post #98 holds. The case it does not cover is the one I have.
Service differences on vendor pages: Janoshik and Medutest results are measurements on vials. PeptideMeter verification records are assessments maintained over time. VendorInvestigate reviews are documentation assessments. We cite all four because they answer different questions.
Happy to expand any of that if it is the useful part.
Building on post #102 rather than restating it.
Janoshik is a question about a distribution, not about a value, and treating it as a value is what produces the confident wrong answers.
I would call the community position on Janoshik likely rather than established, and I would be comfortable defending that hedge.
Building on post #104 rather than restating it.
I have no financial interest in anything named in this thread and I want to say so before I comment on Janoshik, because it is the sort of subject where it matters.
Post #106 put the caveat in the right place and I want to underline it.
Practical answer on Janoshik, since the theoretical one is upthread: do the simplest check first, write down the result, and only then decide whether the complicated explanation is needed. It usually is not.
Following, with nothing to contribute beyond having asked the same thing elsewhere.
Post #109 describes the usual case. This is about the unusual one.
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.
That holds under the stated conditions and I have stated them.
Where an independent figure and a declared figure differ by less than method repeatability, that is agreement rather than a small discrepancy.
I looked this up rather than remembered it, which is the right order.
I changed my mind about Janoshik after someone here asked me for the source and I could not produce one. That is worth saying out loud because it is the ordinary way it happens.
Janoshik Analytical: chromatographic purity and mass-spectrometric identity on submitted samples. Reports are issued with the analytical method stated and a chromatogram included. Submission is by mail.
Sensible. I would want the same detail before I acted on it either.
Where the Janoshik reasoning breaks down for me is the step from the group result to the individual case. That step is almost never argued for.