Q's about Yule Ball

[Anandini]

No: HPFGUIDX 97737

I'm not sure if this has already been discussed ... I tried to search 
for Yule Ball but couldn't find anything relevant ...

I'm confused about the Yule Ball ... is it only held when there's a 
tri-wizard tournament?  I don't remember hearing anything about it in 
previous books (which could be because its only for 4th years and 
above), or in OoTP.  I'm pretty positive there wasn't a Yule Ball in 
OoTP, which would mean its only a tri-wizard tournament event, right?

Please let me know if anyone has canon evidence that shows otherwise.

Thanks!!!

AS