Table 3.

Lack of Significant Differences Between Studies Based on Collection Characteristics^a

Category	Comparison	P value
Study publication date	≤2004 vs >2004	.64
Sources of participants	Clinic vs nonclinic	.12
No. of probands examined	<500 vs ≥500	>.99
Degrees of relatives	First vs >first	.68
Criteria used to diagnose cluster headache	International Classification of Headache Disorders 1 vs other	.64
Methods of diagnosis
In probands	In-person vs not in-person	.15
In relatives	Proband recall vs interview	.63

^aComparisons were performed using the Mann-Whitney U test for all categories. A P value less than .05 was considered significant.