Yeah I forgot that the Xbox One was cheaper for like 9 months. Also, it will be interesting to see what the overall gap change is. The gap grew in 2015.
Actually the gap shrank this year versus last year. Here's how much more the PS4 sold percentage-wise compared to the XBO for the first three quarters of last year and this year, rounded to the nearest 0.1%:
Q1 '14: +30.4%
Q2 '14: +71%
Q3 '14: +59.1%
Overall total: +49.7%
Q1 '15: +31.8%
Q2 '15: +10.9%
Q3 '15: +14.1%
Overall total: +19.1%
The XBO didn't really do well in Q1 compared to last year, but Q2 & Q3 were big improvements. Through the first three quarters of the year, the XBO was up 16.9%, but Q2 & Q3 alone were up 34.3%, though a lot of that was due to how terrible the XBO did in Q2 2014. The XBO was down 6.8% in Q1, up 60.2% for Q2, and up 16.9% for Q3.
Meanwhile, the PS4 was actually down 7% through the first three quarters. You can blame Destiny for that, though. Through the first 8 months of this year the PS4 was up YoY by only 1%, effectively flat, so September alone got the PS4 down YoY. The PS4 was down 5.7% in Q1, up 3.9% in Q2, and down 16.2% in Q3.
Here's how the PS4 & XBO did in 2015 vs. 2014: