Man, other than Mercury, or one of those expensive 3rd party reports I hear about from time-to-time I can't image how you would estimate with any reliability. Perhaps guessing that X % of those using the product, have signed up for an account on the forum?
I would be interested in hearing how you arrive at this ballpark figure...
But 56% of what total number? I think the "...according to IDC" is probably the group that wrote what is hopefully an independent report. But when I have tried to track these things down in the past, I always find out that this type of information cost big bucks.
Interesting how HP throws this percentage about, without any real point of reference. But thats marketing, isn't it? And what exactly is cryptically defined share of "...distributed automated software quality..."? What's being excluded here?
I think you might be on a fools errand Tarun. Whatever number you hang your hat on will probably be pretty mushy.