Another important factor is any lumbar pathologies. Most poeple with back pain have tight hamstrings! It is a clear observation i have seen with all my patients. And by stretching out the hams, a definite relief is felt. Guess the correlation comes from the insertion point of the hams on the pelvis and the tilting positions of the pelvis.

Another factor is the height of the patient (tall have tighter hams!!!) and history of sporting activities (the sporty ones usually have more supple hams as they know the importance of keeping them loose)