Vanadium 50 said:
In this paper, the first error is the combined statistical and systematic errors and the second is the modeling error.
There is almost certainly some correlation between modeling errors and the systematic errors. It is also almost certainly the case than if the degree of this were known precisely, they would have corrected for it.
The correlation between modeling errors and systemic errors probably isn't so great that it is a big problem to use the combined error, although the correlation may indeed be hard to quantify.
The reason to combine the uncertainties anyway is to give you a useable result so that you can evaluate its overall significance. You can combine them explicitly and get a concrete statement about their significance, or you can combine them intuitively which leaves you with a mushier sense of the result's significance that has systemic basis due to cognitive biases in how people intuitively combined uncertainties without doing the math (which tends to overestimate combined uncertainties, especially when they are similar in magnitude).
I would suggest that the biggest reason not to combine them in a paper isn't that you can't do it in a scientifically defensible reason. Instead, one of the important reasons to break out different kinds of uncertainties is to focus in on what is most important to change in the experiment to get more precise results.
If your modeling uncertainty is big, the message is to improve the model.
If your statistical uncertainty is big, the message is to run more iterations of the experiment.
If the systemic uncertainty is big, the message is to look at the chart in the paper showing the different line items that contributed to systemic uncertainty, and then to consider for each one, how easy it would be to improve that line item and how much of a difference it would make if you did.
Breaking out sources of uncertainty has more impact on fellow HEP scientists than the usual paragraph or two of the conclusion to an experimental HEP paper talking about what direction the authors suggest for further research and to improve the experiment, because HEP physicists are numbers people and not words people.
Vanadium 50 said:
You can't really blame the authors for "fudging" when they were not the ones to have combined them.
Certainly. Any "blame" for combining a systemic + statistical uncertainty and a modeling uncertainty by combining the errors in quadrature, is mine in this case.