Coming back to: Specificity, linearity, accuracy, precision, range, robustness — with real criteria posts 91–100

Nothing to add, except that this is the answer I would give if asked.

Taking post #90 at face value and following it one step further.

Range: the concentration range over which the method has been validated. Going outside the validated range is going outside the method's demonstrated performance.

That is the honest state of it as of this week.

I read post #92 twice before replying, because I had assumed the opposite.

What would change my mind on Specificity is a second dataset collected by someone with no stake in the first. Until then I hold it loosely and I would rather say so than pretend to more.

Precision and repeatability: within-run and between-run variability of the method. Acceptance criterion is typically a relative standard deviation of ≤2% for area measurements.

Specificity: the method can distinguish the intended compound from related impurities and degradation products. Tested by comparing results on pure compounds, mixtures of compounds, and degraded samples.

I would put the burden of proof on the interesting explanation, not the dull one.

Everything in post #96 holds. The case it does not cover is the one I have.

Range and working range are different things and a certificate rarely distinguishes them. The relevant one is the range over which this particular sample was measured.

The reasoning is more useful than the number, which is why I have shown it.

Narrowing post #96, because the general version has more than one answer.

A request rather than an answer: could whoever has the primary source for Specificity post it? I have seen the claim three times this month and each version had lost a qualifier.

On post #96 — agreed on the reasoning, with one qualification.

Two things can be true about Specificity 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.

The limit of quantitation determines what the impurity table can honestly contain. Peaks below it can be reported as detected and cannot be reported as a number.