The International Computer Games Association (ICGA), http://www.icga.org/, used to offer a prize for the best-commentating chess program but this did not attract sufficient interest. More recently, and partly because of an increased incidence in computer-aided cheating in human tournaments, there has been considerable activity in rating chess players on the basis of their moves rather than on the, e.g., 'ELO'-basis of the results they achieve in games. There are three approaches here: 1) 'Coincidence'. Notice that a player is playing the same moves as one's computer, searching to depth 'd'. This is the least mathematical way, and uses the least information. It scores a 'coincidence' even if there is no choice of move. It scores a 'non coincidence' if there are two 'equivalent' moves given the same evaluation, and the player chooses one the computer does not choose. 2) 'Average error'. If 'mb' is the best move, and the human loses 'pa' evaluation points (as evaluated by the computer searching to depth 'd') by playing move 'ma', then: Average error = average (pa) This uses more information but again, evaluation of a player is affected when a player plays a move which is the only one available. 3) 'Competence inferred by Bayesian Inference'. This hypothesises a range of stochastic 'model players' which choose a move randomly. The probabilities of choosing a move depend on the evaluation 'pi' of one's computer (searching to depth 'd') and the competence index 'c' of the stochastic players. One then infers the probability of the observed player being stochastic model-player 'i' in the available set of stochastic players. This is the approach I have taken as seen at http://centaur.reading.ac.uk/view/creators/90000763.default.html ... ... anything after 2001 mentioning 'fallibility', 'reference', 'Bayes' etc ... most recently http://centaur.reading.ac.uk/29423/ It uses more information than methods 1-2 and so should be more sensitive/accurate in ranking players - but how much better is not clear. Method 3 would be expected to give very similar results to the method of Ken Regan which uses a range of explicit, parameterised models - consciously trying to model chess-play. Method 1 has inferred that Capablanca played most accurately in his World Championship matches, and he certainly has a reputation for so doing. Capa was, as it were, playing 'The Goddess of Chess' whereas more recently, players have played on their specific opponent's known fallibilities to win - rather than playing the neutrally-objective best-move. At the FIDE Candidates Tournament in London, 2013, the audience were given tablets and a chess-app which compared the two sides' material, mobility, King-safety and overall advantage - an improvement on just giving overall advantage. Guy Haworth