Almost infinite amount of variables to that question, and most of them we don't even know...
Species of anemone - Some rarely, if ever split, being the biggest...
Of the "frequent splitter" varieties, some theorize that they split when they're healthy, to increase their numbers. However, there's another school of thought that believes they split when they're extremely unhealthy, and "think" they're dieing, to increase their chances of survival.
I personally subscribe to the 2nd theory, which would explain why we so often see splits after large water changes, or when a specimen has been moved (Which, from the animal's point of view is pretty similiar to a large water change).
I've got a green BTA that I've had for around 7 years now... It used to split on me at least once every 3 months, like clockwork, for years...
It's been in the dedicated anemone display tank for a year or so now, and hasn't split a single time.
So, in summary... There's really no way to know how often a particular anemone will split, or why they do either. Some anemones will split often (every 2 months or so) for some people, and never split for someone else...
(Disclaimer - I'm not saying people who have frequent anemone splits have bad tanks, please don't misunderestimate my comments!
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