Re: Are graded clinical signs more reliable than dichotomized?

Roland wrote:

Instead of dichotomising these clinical signs I think that a grading
of the intensity of the sign must retain more of the diagnostic
information

Correct

One problem is of course that there is no definition for the grades of
the variable. However the dichotomised variable has the same problem

Correct

and I assume that the agreement between two examiners will be larger
if graded variables are used instead of dichotomised.

No. There will be *more* agreement with *fewer* categories. The fewer
the
categories, the less opportunity for disagreement.

I tend to agree with those who suggest that having more categories is
better
from a *research* or *statistical* standpoint. But clinical practice
evolves
to optimize several factors. Some are optimized by having more
categories,
some by fewer. There is a tradeoff, and the solution to the tradeoff
is
different for each application.

I believe there is such a tradeoff between
reliability/agreement/reproducibility (better with fewer levels) and
accuracy/precision (better with more levels).

The solution to this tradeoff is different for each application. That
is why we see staging in some areas, but yes/no distinctions in others.

One example where dichotomous ratings might be better is a screening
test. It is logistically better to screen patients into two groups.
Then a more refined test can be given to those who screen positive.

Hope this helps.
--
John Uebersax PhD

.