Does a smaller cage increase the chance of finishes?

While my eyes have been telling me Apex's smaller cage results in more action, there's not enough evidence to support the idea of significantly higher finish rate. To be clear, I'll argue the finish rate is not significantly higher, statistically we see that the rate is marginally higher.

The UFC has been hosting fights in their Apex complex in Las Vegas with no fans, weeks after the Covid-19 pandemic forced them to shutdown fights briefly. The Apex's octagon is of 25 foot diameter, where as the octagons mostly used before are of 30 foot diameter. Although 5 feet of diameter may not sound like much of a difference at the first glance, once you do the math, it means the smaller octagon is of 30.5% smaller size than the one we're used to watching fights in! This is a significant difference in the octagon size.

The main reason to argue against significant higher finish rate is that we haven't had a big enough sample size of fights in smaller octagons to compare them to years of fights in bigger octagons. The finish rate in the 30 foot octagon was about 44.4% for 2020 pre shutdowns. The rate in the small octagon were once near 60%, simply because of very few fights that happened had more KO/TKOs than usual. The rate is now (as of July 7th 2020) about 52.7% since the shutdowns, which is much closer than the large octagon's. The 8.3% is not significant, but undeniable as we're looking at the same athletes on the UFC roster fighting in both octagons. We're not looking at different eras or promotions of fighters.

Aside from the sample size, we need to think about the fights that have been happening too. The finish rate is not the same in all divisions (weight class and gender combination) of the UFC, so the data can be skewed too. And so for a deep dive down of the effects of the finish rate and the octagon size, one should really break it up on a divisional basis. Two flyweights fighting in a 30 foot octagon have ton more space than two heavyweights in the 25 foot octagon. Also remember different athletes have different styles, some are more likely to KO or submit an opponent than others. The fighters on Apex cards also make a difference on the finish rate. So to truly have a meaningful amount of data to analyze the finish rate in smaller octagon we needs months if not years of fights in the smaller octagon with each athlete fighting multiples times in both cage sizes.

The origins of the UFC 25 diameter octagon is the WEC which was purchased by the owners of the UFC and merged to the UFC, with the larger octagon size being set as the standard. The smaller octagon is also used in Dana White's Tuesday Night Contender Series, and The Ultimate Fighter. While the WEC had higher level athletes than UFC in some divisions - specially in women's as the UFC lacked any female divisions - the latter 2 mentioned fights are between lower level fighters. So looking at data for the smaller cage size pre 2020 shutdowns should be done with a grain of salt.

One last thing to remember is take into account the pandemic itself. Was everyone able to train as they wished with the gyms closing? Did they end up fighting a different opponent than their trained? Had they fought in a smaller octagon before?

Lastly, here is an article from 5 years ago analyzing the cage size and finish rate. This is not the first time this debate has come up. Since the article is somewhat older, the data has nothing to do with the Apex fights.