Second pass at: Robustness: the parameters worth deliberately varying posts 61–67

This follows post #60 rather than contradicting it.

The most useful single question about a method: what would it fail to detect? Every method has an answer and few documents state it.

That is what the documentation says. What happens in practice is usually close.

I have no financial interest in anything named in this thread and I want to say so before I comment on Robustness, because it is the sort of subject where it matters.

Acknowledging rather than arguing. The reasoning holds as far as I can follow it.

Coming back to post #62, because the follow-up matters more than the original answer.

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.

Taking post #64 at face value and following it one step further.

Genuine question rather than a rhetorical one: has anyone here actually observed Robustness, as opposed to read about it? The thread is long and I cannot tell.

Post #62 and I disagree about the size of the effect, not about the direction.

Robustness is a question about a distribution, not about a value, and treating it as a value is what produces the confident wrong answers.

Forced degradation studies: deliberately stress the material with acid, base, oxidant, heat, light to generate degradation products and demonstrate that the method can separate them from the parent peak. Acceptance is that the method is stability-indicating.

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