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I was looking at the statistics for my tournament games in SCID, and found something surprising. When I played opponents rated under 1000, 13 out of 15 times I've had White. Conversely, when I played opponents rated 2000 or higher, 10 out of 15 times I've had Black.

I'd accept 10 out of 15 as being coincidence. But 13 out of 15 seems unlikely to happen purely by chance; the odds are less than 1%.

Is there a reason why a person would tend to play stronger players as Black and weaker players as White? Or is it just a coincidence?

3

Your 1% chance calculation is wrong, because "observations" are not independent from each other within a single tournament. When you play one round as White, you are very likely to play the following one as Black. Also, after a win, you are very likely to face a stronger player in the next round. So your tournament could go something like this.

WHITE, weak opponent. WIN

BLACK, strong opponent. LOSE

WHITE, weak opponent. WIN

... (you get the idea)

This means that if, in 3 consecutive tournaments, you get to play a weak opponent as White (let's say that, by ranking, you are about 100th in a pool of 200 players), you can easily get pairings such as those you are showing (with a 1 in 8 chance, and also a 1 in 8 chance of getting the exact opposite)

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  • Thanks for giving a plausible explanation as to how it could more easily happen by chance. But looking at my 15 games against low rated players, there are just four that occurred after I had already played a sub-1000 player sometime in that tournament. Of those four, two came after I had won the previous round, and one came after I drew the previous round. So that doesn't seem to be why it's happening for me, for the most part - at most it explains one game. – D M Jul 8 '19 at 21:41
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Is there a reason why a person would tend to play stronger players as Black and weaker players as White?

No

Or is it just a coincidence?

Yes.

To understand this you only have to look at the way the first round of a Swiss tournament is drawn. Following rounds follow similar principles within score groups (groups of players with the same score) and allowing for colour preference (aiming for WBWBWB etc and avoiding BBB and WWW except possibly in the last round).

Suppose you have 16 players who we'll call for simplicity's sake "1", "2", ... "15", "16" where "1" is the strongest, "2" next strongest and so on. Colour for the first round is determined randomly, that is half the time player "1" gets black and half gets white.

The first round draw should look like this when "1" is assigned white:

"1" v "9"
"10" v "2"
"3" v "11"
"12" v "4"
"5" v "13"
"14" v "6"
"7" v "15"
"16" v "8"

As you can see half the time the weaker player is white and half the time black.

When you see deviations in this pattern it tells you one of two things:

1) There was a forbidden pairing which changed the order
2) One or more players who entered the tournament pulled out or missed the first round without telling the arbiter and some pairings were redone to try and ensure that every player had a game.

Note that 2) requires either the agreement of the players involved in the redraw or that the tournament conditions specify that this will happen automatically. The chess world's leading barrack room lawyer, now a FIDE vice president, famously pulled out of a tournament when this happened to him in the first round without his permission and without being part of the tournament conditions.

Occasionally you will see a (high level) tournament where the tournament appears to have been split in two with the top half paired according to the above algorithm and the bottom also paired accordingly. In this case something called "acceleration" has been applied to keep the strongest and weakest players apart for the first round or two. This is done in norm tournaments where the chances of norm seekers in the top half of the field would be ruined if they had to play 2 or more very weak (relatively) players in the early rounds.

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  • "As you can see half the time the weaker player is white and half the time black." - Clearly that's true in the first round. If I throw out the first round games (which should be totally random as to colors) I'm left with 5 of 10 as Black in my 2000+ games, which does eliminate the effect. But I'm still left with 12 of 13 as White in my under-1000 games. – D M Jul 6 '19 at 1:09

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