Basebology (The Study of Baseball): Joe Sheehan confirms my bias about confirmation bias

Wednesday, April 15, 2009

Joe Sheehan confirms my bias about confirmation bias

Sometimes being right isn't all that much fun; as arrogant as it is to say this, I'm fairly familiar with the concept. Let's be clear, too, that this applies when the first week of the season confirms my biases. The Astros are a bad baseball team that probably has the worst bottom 20 roster spots in MLB; that they're 1-5 with the worst run differential in baseball doesn't tell us much more than we knew a week ago. Just because a small sample confirms your pre-season analysis doesn't make it any more valid.

Bingo.

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Key Stats

ARP
Adjusted Runs Prevented

ARP measures the amount of runs that a relief pitcher prevented from scoring above what an average relief pitcher would have prevented. ARP is adjusted for the situation in which the pitcher was used.

ISO
Isolated Power

ISO is the ratio of extra bases that a player has accumulated to the number of at bats he has received. ISO is essentially a player's SLG minus his batting average. This has the effect of giving a player credit only for extra base hits. ISO is not a useful measure of player value on its own, but is a very effective measure of a player's extra base ability.

OBP
On Base Percentage

OBP is the ratio of the number of times a player reached base safely to the number of opportunities he had to reach base. It effectively measures a player's skill at not making outs. Since outs are a teams most precious commodity, OBP measures perhaps the most valuable and fundamental skill a player can have.

OPS
On Base Plus Slugging Percentage

OPS is a crude metric that simply sums a player's on base and slugging percentages. It is probably the most popular non-traditional measure of overall batting performance due to its simplicity. However, it has drawn criticism from performance analysts for its inaccuracy relative to other advanced metrics and because it works by adding two numbers with different denominators together to produce a conceptually meaningless quantity. It is best used as a quick and dirty estimator of batting prowess.

SLG
Slugging Percentage

SLG is the ratio of total bases that a player has accumulated to the number of at bats he has received. It is essentially a weighted batting average that gives a player more credit for extra base hits.

UZR
Ultimate Zone Rating

UZR is a defensive metric that uses play-by-play data to determine how good a player's defense is. On Fangraphs, it is denominated in runs saved above average.

VORP
Value Over Replacement Player

VORP measures the amount of runs that a player contributed above what a "replacement player" at the same position would produce. VORP considers only offensive contributions.

WARP
Wins Above Replacement Player

WARP measures the amount of wins that a player contributed above what a "replacement player" at the same position would produce. WARP considers both offensive and defensive contributions.

WXRL
Win Expectancy added above Replacement adjusted for Lineup

WXRL measures the amount of wins that a relief pitcher contributed above what a "replacement player" would produce. WXRL differs from WARP because it is adjusted for both the game situation in which the pitcher was used and the hitters that the pitcher faced.

Basebology (The Study of Baseball)

Wednesday, April 15, 2009

Joe Sheehan confirms my bias about confirmation bias

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