There are innumerable questionnaires for dizziness, and the DHI is a popular one.
The dizziness handicap inventory was developed by the same authors who developed the tinnitus handicap inventory, (Jacobson et al, 1990).
The DHI is not a diagnostic test -- rather it produces scores related to the perceived dizziness handicap -- a subjective quantity.
The DHI is a 25 item test, and the maximum score is 100.
We also have a large repertoire of dizzy patients in our clinic practice , where we have obtained the DHI in a bit over 5000 of them. .
Unlike the situation with the THI (also developed by the same authors), this questionnaire looks as if it has some reasonable statistical properties. It looks somewhat like a normal curve, it is not very skewed like the THI. Now the scores above are not from normal control subjects - -these are people who are endorsing dizziness. They are claiming to be dizzy. So one cannot really say that it is "abnormal" to have such and such a score, but one can certainly say that among dizzy patients, most have a score of about 40, and it is very unusual to have a score of 100, but not so rare to have a score of 0.