Ratbastard, by your analysis, there should be 490 (98 posts per thread average x the 5 threads) in sports threads in all of 2015. 3/4ths of the way thru, by my quick count (seeing at what page the threads clicked over to 2015 posts, then counting number of pages to the end and multiplying by the number of posts the software puts per page, 15 by my settings) there have actually been 715 posts so far. I wouldn't exactly say your methodology is doing a very good job of estimating the 2015 post counts, or current traffic, in sports vs music threads which was what Sidehatch was asking about.
Its almost like, I don't know, your model doesn't normalize time as a variable to take into account that there might be a different number of active posters during different years on the board or something. *shrug*