The general method is Monte Carlo Simulation. Basically I've set up a spreadsheet which allows me to simulate the results of the German Masters & Welsh Open and model the impact on the rankings. By simulating this a number of times (e.g. 10,000) you hope to get a reasonable approximation to the true probability.
The main input is an estimate of the probability that one player will beat another. For this I've used my Snooker Ratings (
http://www.snookeranalyst.com/current-ratings/). For example, Ronnie has a rating of 1,099 while Joe Perry has a rating of 749. You would therefore expect Ronnie to win 1,099 / (1,099 + 749) = 59% of frames won between the two. Making an assumption that the result of each frame is independent of one another (which probably isn't true, but is a reasonable simplification) then this equates to Ronnie winning 72% of "best of 9 frame" matches that they play.
On that basis you would certainly expect him to beat Perry and he has a reasonable chance of progressing further in the German Masters. Walden's rating is lower at 783 and given that he also has to play a qualifying match, you would expect (on average) Ronnie to collect more points than him in the Welsh Open.
The main question around this analysis is how accurate the ratings (based on historical results) are at predicting the results of specific matches in the future. Ronnie certainly looks over-rated given his lack of form in full ranking events over the last couple of years, although his form in the PTC events was very good. That said, his head to head record against Perry shows that he has won 61% of frames (49 out of 80) and 86% of matches over different lengths (6 out of 7).
Ultimately the 55% estimate is fairly meaningless because in real life it's down to the results on the day, but at least it provides a reasonable indication of how things might play out if each player performs close to their typical level of play.
