When the UFC debuted in 1993, the finish rate was 100%, as there was no other way to end the contest. It was not until 1995 that time limits debuted, and eventually decisions.
20 years later, in 2013, the rate declined to 50% EXACTLY - of 176 fights to date in 2013, 88 have been finished by TKO/KO or submission.
While fans of the HOLY F@$%ING $#!^ moments that make the sport so compelling may look at the stats with dismay, the decline has now stabilized at 50%, for years.
It was the institution of weight classes that give us the best insight into the trends during the modern Zuffa era. When finish rates hit a decade high of 75% in 2005, it was the first full year the UFC went without lightweight fights. Lightweights were officially brought back in 2006, and by 2007 the division became the most commonly competed weight class, with more fights taking place at 155 pounds than in any other division. (That has remained true every year since.) Rebounding in 2008, the finish rate hit 68% in a year where slightly more fights occurred in heavier divisions than in years prior. But this composition of divisions quickly went on a diet, and over the next two years fighters began migrating down weight classes and tilting the scales towards smaller divisions.
This period in 2009-2010 saw the greatest decline in finish rates combined with the rapid increase in televised UFC events, and likely an overall increase in the competitiveness within the UFC. In 2010 the first featherweights were introduced before the year’s end, with the WEC merger taking full effect in 2011. By 2012 the first flyweights hit the Octagon, and by then half of all UFC fights occurred at lightweight or below.
The most interesting trend to note is that despite the slimming trend for UFC fighters, the overall finish rate has completely stabilized since 2010. As we saw earlier smaller divisions generally finish fewer fights, due primarily to less knockout power, but the dropoff stabilizes in the smallest divisions. So despite more and more fights in the flyweight through featherweight divisions, the finish rate is no longer dropping with the declining share of heavier fights.