Coming back to: Specificity, linearity, accuracy, precision, range, robustness — with real criteria

Narrowing post #15, because the general version has more than one answer.

The number people quote for Specificity is a central estimate presented without its interval, and the interval is wide enough that the estimate is nearly uninformative on its own.

No notes. Posting so the count is not one.

I would keep Specificity 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.

Robustness: the method gives consistent results when minor parameters vary. Tested by deliberately varying pH, temperature, flow rate, and mobile phase composition within reasonable ranges and demonstrating that results stay within acceptance.

This is the version I would want a new member to read first.

Agreed on Specificity, with one qualification that I think matters. The reasoning holds for the case as described. Change the starting assumption and it does not, and the starting assumption is the part nobody states.

Linearity: the detector response is proportional to compound concentration across the working range. Demonstrated by running standards at multiple concentrations and showing R-squared values typically ≥0.99.

A method that reports the same number for every lot is worth a second look. Real processes vary, and a total absence of variation is a statement about the measurement rather than the process.

Not a conclusion. A place to stand while looking for one.

One more thing on Specificity that took me far too long to see: the two figures people quote are not measuring the same quantity. Once you notice that, the apparent contradiction disappears.

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