The Tournament Strength Index is an indication of the event's significance in the overall chess-playing community. For example, an event involving 25 average players is generally more "significant" than a Quad of average players. An event with 100 strong players is generally more important than one with 25 strong players, and so on. Also, an event among high-rated players is considered more important than one (all other things being equal) than one with low-rated players. An event with more rounds (more games played) has more significance than one with fewer rounds (all other things being equal). Finally, an event with a slow time control would generally be considered more important than one with a fast time control.
A Significance Index is calculated separately for each Section (Section Significance Index - "SSI"). The highest SSI in any tournament is called the TSI. This is often the strongest section's SSI, but not necessarily so, as a lower section may have much larger participation or other overriding factors. Sections with fewer than 3 rounds or an effective** average rating below 400 or effective* number of players less than 4, do not qualify for an SSI.
*Effective numbers reflect games actually played in a section. For example: suppose that 16 players have registered for a 5 round event. Suppose one of the players had to leave suddenly, before round 1. With 15 remaining players, there are going to be several BYEs. Also, some of the players may show up too late to play round 1, or some players may have to leave early, not playing the last round or two. Thus, instead of the theoretical maximum of 40 games, the event might have only, say, 30 games actually played. The effective number of games is 30, not 40. If only 30 actual games were played in a 5 round event, that means only 6 games were taking place, on average, in each round. Since 6 games involves 12 players, the effective number of players in this section becomes 12, not 16. Similarly, suppose that the average rating of the 16 registered players is 1622. What if some of the top-rated players were those (for whatever reason) playing fewer rounds than anticipated? The effective average rating is calculated based upon games actually played. In the situation suggested above, the effective average rating might be something like 1593 instead of 1622, since fewer of the games actually played involved the higher-rated players.
Average rating often is not the best measure of what it takes to win a given section, however. Consider that to be a contender, a player needs to score well in the early rounds. Having done so means he is probably going to face stronger-than-average players in the following rounds, and -- if he continues to do well -- he will almost surely face another strong contender in the last round. Thus, the winner of a section will generally have faced players with higher ratings than the section average. In order to take this effect into account, CXR has come up with what it calls the "Contention Rating". We use this to improve our formula for SSI (and TSI), by taking the higher of: (a) the game-weighted average rating, or (b) the Contention Rating.
TSI is a proprietary metric, and CXR is the only rating authority that provides this measure of tournament significance. Please ask your local tournament director to contact us to obtain a TSI for his or her events.