We want to explore the cross sectional association of 5 symptoms of psychopathology with functional impairment.
If we just take people who score high on symptom 1, then high on symptom 2, etc., and look at the means of social impairment in these groups, one particular symptom (let's call it symptom 1) stands out that is associated with very high functional impairment (twice as high as the others).
The problem is that this is confounded with the sum score of all symptoms, because people who score high on symptom 1 have high scores on all other symptoms as well. This is different from all other symptoms. People who score high on symptom 2 only have average symptom load on the other symptoms (the same for symptom 3, symptom 4, etc).
I wonder (1) what test would be appropriate to test this, and (2) how one would control for the fact that for one symptom the sum of other symptoms seems particularly high.