selection bias
#test-results 2026-03-30
Monday41 messages10 participantstimes are UTC
Highlights from this day
- subq_sy — quantity testing is usually a separate line item and it is the one worth paying for, i think 09:11
- food_noise_off — underfill is more common than impurity. if you only test purity you are testing the less likely failure 10:39
- HPLC_Hank — the results in this channel skew because people test when they are suspicious. that is selection bias and it is real 13:36
right so is anyone tracking results over time in a way they would share
a point or two between the certificate and an independent result is inside what two labs disagree by
genuine question a result without a lot number and a purchase date is an anecdote with a pdf attached, ymmv
i told GL Biochem about a result they would not have liked and they did not argue. credit where it is due
a point or two between the certificate and an independent result is inside what two labs disagree by
[edited]if you are testing to settle an argument you will not settle it with n of 1
nice result
sample handling on your end absolutely affects it. draw cleanly, ship fast, do not let it sit warm
coming back after 4 months with a follow up result, where do i put it
my vial assayed under label but the purity was fine, which matters more
posting my Medutest result on lot F-1330, what do people make of it
quantity testing is usually a separate line item and it is the one worth paying for, i think
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weigh the vial before you reconstitute. it costs nothing and catches the common failure
my sheet has 4 lots from WWB with a spread under a point, which is tight
how do you post a result so it is actually useful to somebody in a year
update from 26 months ago: retested the same supplier, result came back better, logged both
Digest for the week of 2026-02-21 has been published.
is it worth testing if the vial has already been through a warm transit
log the lot number
underfill is more common than impurity. if you only test purity you are testing the less likely failure
🙏5
weigh it first
attach the pdf
thats within range
whats the lot
a supplier disputing a result is rare here and it has never gone well for the supplier
when did you buy it
assay under label with good purity means you got less of the right thing. that is a fill problem, not a synthesis problem
99.4 against a certificate of 99 is fine. the same supplier landing low four times in a row is a question
one data point
log the boring results too. a channel that only records failures produces a false picture
my read after three years of this: purity is mostly fine across the market and fill consistency is where suppliers differ
the results in this channel skew because people test when they are suspicious. that is selection bias and it is real
fridge-thermometer.png
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*that should say weekly
quick one what interests me is when the gap goes the same direction every time. once is noise, three times is a pattern
follow up a single sample tells you about a single vial. that is genuinely all it tells you
one bad test does not condemn a supplier. one good test does not clear one. both halves get ignored equally
the honest limits: hobby chain of custody is weak and any result here should be read with that in mind
thats not great
thats a fill problem
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whats the underfill rate people are actually seeing
i had a result i am fairly sure was a handling error on my side and i logged it as such
if the vial has been through a bad transit you are testing the transit as much as the supplier
[edited]