We also have an online survey instrument that does MIDAS here.
The MIDAS test is not a diagnostic test for headache but rather it measures the severity of already diagnosed headaches. It is similar to the HIT-6 test, but it emphasizes duration and frequency. It was developed to measure response to medication, and not to diagnose the type of headache.
The MIDAS test mainly measures duration -- it asks questions such as "On how many days in the last 3 months did you miss work or school because of your headaches? ". If you missed every day -- your score for this question alone would be 90 !. There are 5 questions like this, so a total of 450 !
The MIDAS tests is graded as "Severe" for 21 days or more. Thus the MIDAS test has a gigantic space for "severe" -- between 21 to 450.
This histogram is from a very large # of patients who were tested with dizziness in our practice in Chicago. Many of these patients may not have been complaining of headaches at all. Thus it is not surprising that the largest number of subjects have a score of 0. It is disturbing however, that the scores are not at all distributed "normally", or in other words, like a bell curve. Rather, they seem to be less and less people who endorse having many days of symptoms. There are many people who score above 21, which is the "severe" group, at least considering this sample which is pretty diverse.
Validity means that it is statistically robust. It does not mean it is useful. From our discussion above, it is clear that the MIDAS test is not a diagnostic tool -- it is a severity tool, best suited for quantifying response to treatment.