What percentage of doubleheaders are swept?

This question originated from the (dis)advantage that the REd Sox had by having their Monday night game rained out, while the Yankees played. I heard this stat for the first time yesterday and was suprised by it. The stat bureau indicated that a majority of baseball insiders were shocked by it as well. Correct answer to be posted later.

FYI: Stat reported on doubleheaders since 1990's through present.

[DougOzzzz]

I completely misread this and voted "20-30%" thinking how often 1 team would sweep the other. The answer should be either 40-50% or 50-60% (probably the latter).

I would be surprised by anything outside that range, but I'm not sure how large the sample size is.

[Paluka]

This stat was posted today or yesterday on joyofsox.blogspot.com

[hoopsie44]

[ QUOTE ]
I completely misread this and voted "20-30%" thinking how often 1 team would sweep the other.

[/ QUOTE ]

Isn't this what the OP is asking?

[ QUOTE ]
[ QUOTE ]
I completely misread this and voted "20-30%" thinking how often 1 team would sweep the other.

[/ QUOTE ]

Isn't this what the OP is asking?

[/ QUOTE ]

Yes. How often are both games won by the same team.

i should give credit -- heard it on WFAN 660 AM new york

[Benholio]

[ QUOTE ]
[ QUOTE ]
I completely misread this and voted "20-30%" thinking how often 1 team would sweep the other.

[/ QUOTE ]

Isn't this what the OP is asking?

[/ QUOTE ]

The OP means by either team, I think the reply mistook him for any certain team (like say, the home team).

[jdl22]

I voted 20-30 which is absurd.

If two equally skilled teams play two in a row and the outcome of the first doesn't affect the second then the probability of a sweep is 1/2. If the teams are less evenly matched the probability is higher. Also, I think winning the first game would make a team slightly more likely to win the second because the other team's bullpen probably got more use so they wouldn't have their best guys in there the second go. I'm going to guess 75%.

[RR12]

I can't remember where I read the stat yesterday, but it was to disprove the old idea that it's harder to win both games in a double header than back to back games. Since 1990 there has been 340 double headers and the team that won the first game won the second game 51% of the time. In the same time frame the team that won the first game of any series won the second game 51% of the time. There is really no difference to games played in the same day or not.

PS: paluka are you originally from Indiana?

[sam h]

Must be 50-60. If the teams are evenly matched and the first game doesn't affect the second, it will be 50%. Effects of one game on the other are hard to determine and probably negligible as far as sweeping goes. But unevenly matched teams will nudge the sweep percentage up. For example, if one team has a 60% chance to win each game, then the sweep percentage is 52%. If one team has a 55% chance, then the sweep percentage is about 50.5%

Edit: 50.5-52% is probably a good guess, as the better teams in games, on aggregate, will likely have somewhere between 55% and 60% chance of winning.

[Homer]

If two teams are equally matched, it's 50%, but most of the time it's probably 60/40 or so, which makes it 52%. So I'll go with 52%.