The HIT-6 is a 6 item screening instrument to quantify headache. A link to a PDF of the HIT6 is here. This questionnaire is fast -- there are 6 questions, with a maximum # of points of 6*13 (78). Scores above 50 are "high".
The HIT-6 is used for all kinds of headaches, not just migraine. It does not differentiate among different kinds of headaches -- it measures impact of a headache. In other words, the HIT will not tell you whether your headache is from a brain tumor or a migraine, but it could tell you whether your headache is significant (i.e. high score), or changing (i.e. difference in scores over time). It has been translated successfully into many languages (Martin et al, 2004; Gandek et al, 2003).
The HIT-6 is fast enough that it can be used to decide if a treatment is working -- According to Castient et al (2012), Improvement can be concluded if the HIT score in tension headache decreases at least 8 points. It seems likely that other headaches react similarly.
These scores came from a large number of patients seen in the author's medical practice, largely for dizziness, but some for headaches. Unlike the unfortunate situation with the MIDAS questionaire, these scores do look somewhat like a bell curve. There is an obvious preference for certain answers resulting in those spikes. This is just to give you a general idea of what to expect. These were not normal subjects.
Yang et al (2011) reported that in a total of 2,049 survey participants, participants were identified as 6.4% CM (Chronic migraine); 42.1% EM (Episodic migraine);and 51.5% non-migraine, with respective mean HIT-6 scores: 62.5 +/- 7.8; 60.2 +/- 6.8; and 49.1 +/- 8.7.
Rendas-Baum et al (2014) found it valid in chronic migraine.
In the graph above, it can be seen that mean HIT-6 scores in dizzy patients are about the same as chronic migraine patients. So this would make one wonder if it is measuring really measuring headache, or questionnaire taking behavior.