Background Losses- Sum of Context-Dependent Player Losses (pLosses) for a Team minus Team Losses; equal to one loss per Team Game played.

Background Wins- Sum of Context-Dependent Player Wins (pWins) for a Team minus Team Wins; equal to one win per Team Game played.

Ballpark Factors- Factors which measure the relative likelihood and/or value of certain events, including run-scoring, across different ballparks within the same league and season. Ballpark factors are typically expressed as indexes, relative to 100, reflecting differences in average runs scored in the ballpark relative to league average. The calculation of Ballpark adjustments used in my work is described here. Ballpark factors calculated by me are presented here.

Base-Out Probability Matrix- Matrix showing the probability of transitioning from a particular starting base-out state to a particular ending base-out state. Calculations of base-out probability matrices are described here.

Base-Out State- Number and location of baserunners and the number of outs at the start of a particular plate appearance. There are 24 possible initial base-out states; 28 possible ending states (the ending state may include 3 outs; the 4 ending base-out states associated with 3 outs vary based on the number of runs that scored on the inning-ending play, 0 - 3).

Baserunning Losses- Losses accumulated by a player as a baserunner.

Baserunning Wins- Wins accumulated by a player as a baserunner.

Batting Losses- Losses accumulated by a player as a batter.

Batting Wins- Wins accumulated by a player as a batter.

Component- Each of the nine steps in the process of calculating Player won-lost records.

Component 1- Basestealing (stolen bases, caught stealing, pickoffs, balks). Component 1 decisions are assessed to baserunners, pitchers, and catchers.

Component 2- Wild pitches and passed balls. Component 2 decisions are assessed to baserunners, pitchers, and catchers.

Component 3- Balls not in play: strikeouts, walks, hit-batsmen. Component 3 decisions are assessed to batters and pitchers.

Component 4- Balls in play, including home runs. Component 4 decisions are assessed to batters and pitchers.

Component 5- Hits vs. Outs on balls in play. Component 5 decisions are assessed to batters, pitchers, and fielders.

Component 6- Singles vs. Doubles vs. Triples on hits in play. Component 6 decisions are assessed to batters, pitchers, and fielders.

Component 7- Double Plays. Component 7 decisions are assessed to batters, baserunners, pitchers, and fielders.

Component 8- Baserunner Outs. Component 8 decisions are assessed to batters, baserunners, and fielders.

Component 9- Baserunner Advancement. Component 9 decisions are assessed to batters, baserunners, and fielders.

Context- Importance of a specific play in terms of determining team victories relative to a play of average importance.

Context-Dependent- Player decisions calculated such that player wins and losses are tied to team wins and losses. The calculation of context-dependent player wins and losses (pWins and pLosses) is explained in detail here.

Context-Neutral- Player's expected record if his performance had happened in a typical context with average teammates. The calculation of context-neutral player wins and losses (eWins and eLosses) is explained in detail here.

Correlation- Relationship between two series, expressed as a number between -1 and +1. A correlation of 1 means that two series move perfectly together - literally, if two series have a correlation of 1 it means that one of them can be expressed as a linear function of the other. A correlation of 0 means that there is no relationship between the two series. A correlation of -1 means that two series move in exactly opposite directions.

DIPS- Defense-Independent Pitching Statistic. DIPS measures expected Earned Run Average as a function of only those events which are not affected by defense: strikeouts, walks, hit batsmen, home runs. DIPS was developed by Voros McCracken based on a theory that major-league pitchers have very little, if any, control over balls in play.

e- Prefix meaning "expected". Statistics with an "e" prefix have been adjusted to reflect expected performance in a typical context with average teammates.

eLosses- Player's expected losses if his performance had happened in a typical context with average teammates. The calculation of eLosses is described here.

Event Probability- Probability of a particular event occuring. For example, the probability of a particular ball in play being a triple, given the hit type (ground ball, fly ball, line drive) and location of the hit. The calculation of event probabilities is described here.

eWins- Player's expected wins if his performance had happened in a typical context with average teammates. The calculation of eWins is described here.

eWOPA- Wins over Positional Average (WOPA) calculated using eWins and eLosses.

eWORL- Wins over Replacement Level (WORL) calculated using eWins and eLosses.

Expected Context- Expected context. Expected product of inter-game and intra-game context based on the position(s) played by a player. The calculation of Expected Context is described here.

Expected Win Adjustment- Expected intra-game win adjustment based on player's individual performance, assuming that the rest of his team consisted of average major-league players. The calculation of Expected Win Adjustment is described here.

Extrapolated Games- Retrosheet has released some seasons for which they only have play-by-play data for some games. For these seasons, Player won-lost records for missing games can be extrapolated from Player won-lost records for the games for which Retrosheet has released play-by-play data. See here for further details.

Fielding Losses- Losses accumulated by a player as a fielder.

Fielding Wins- Wins accumulated by a player as a fielder.

Harmonic Mean- The Harmonic mean of A and B is equal to 2*(A*B) / (A + B). Frequently, in my work, the 2 in the above formula would end up dropping out, so I simply use (A*B) / (A + B).

Hit Type- Type of batted ball for a ball in play: bunt, ground ball, fly ball, or line drive.

Inning Probability Matrix- A matrix indicating the probability of a team winning a game given the specific lead/deficit at the start of a particular inning. The calculation of Inning-Probability Matrices is described here.

Inter-Game- Within a single game. Relative importance of situations within the same game on that game's final outcome.

Inter-Game Context- Inter-game context measures the average importance of the situations in which the player participated within the context of the game. Inter-game contexts are discussed in more detail here.

Inter-Game Win Adjustment- Adjustment to player's winning percentage based on the timing of his performance within games. Inter-game win adjustments are discussed in more detail here.

Intra-Game- Across games. Relative importance of situations within one game as compared to the importance of comparable situations across all games.

Intra-Game Context- Intra-game context normalizes player decisions so that total player decisions are equal across all games. Intra-game contexts are discussed in more detail here.

Intra-Game Win Adjustment- Adjustment to player's winning percentage based on the timing of his performance relative to his team's performance. Intra-game win adjustments are discussed in more detail here.

Leverage- Relative importance of a situation. Conceptually, leverage is the same as inter-game context, as I use the term. Leverage was developed by Tom Tango.

Linear Weights- Run-scoring estimator which is constructed by estimating the number of runs generated by each possible offensive event (single, double, triple, home run, etc.). Summing up this value for each event generated by a player or team then represents an estimate of the total number of runs generated by that particular player/team. Linear Weights were first developed by Pete Palmer for his series of Total Baseball books.

Losses- Player decisions which contribute toward the player's team's probability of losing.

Net Wins- Total Player wins minus Total Player losses associated with a particular play or plays. Net wins for various events are described here. Net wins for various events by season by league derived from my work are presented here.

p- Prefix standing for "Player". Statistics with a "p" prefix are adjusted such that player wins and losses tie to team wins and losses.

Pennant Probability- Probability of a team winning the pennant, given their current record, the current records of their opponents, and the number of games remaining in the season. The relationship between Win Probability and Pennant Probability is discussed here.

Persistence Equation- Equation measuring the extent to which a statistic (typically, a Player's won-lost winning percentage in my work) persists over time. The persistence of a statistic can be viewed as the extent to which something represents a real "skill" as opposed to being the result of simple random chance. Persistence equations are described in more detail here.

Pitching Losses- Losses accumulated by a player as a pitcher. This is not to be confused with the traditional baseball statistic, pitcher losses.

Pitching Wins- Wins accumulated by a player as a pitcher. This is not to be confused with the traditional baseball statistic, pitcher wins.

Playoff Probability- Probability of a team making the playoffs, given their current record, the current records of their opponents, and the number of games remaining in the season.

pLosses- Player losses calculated such that player losses are tied to team wins. For a team, the sum of player losses will be equal to team losses (plus 0.5 pLosses per tie game) plus team games played. The calculation of pLosses is described here.

Positional Average- Average winning percentage expected for a player who played the same position(s) as a particular player. The calculation of Positional Averages is described here. Positional Averages by position by season are presented here.

Positional Replacement Level- Replacement Level performance of freely available players who could have been found to play the same position(s) as this player. Set equal to one standard deviation below Positional Average. Positional Replacement Levels by season are presented here.

pWins- Player wins calculated such that player wins are tied to team wins. For a team, the sum of player wins will be equal to team wins (plus 0.5 pWins per tie game) plus team games played. The calculation of pWins is described here.

pWOPA- Wins over Positional Average (WOPA) calculated using pWins and pLosses.

pWORL- Wins over Replacement Level (WORL) calculated using pWins and pLosses.

Replacement Level- Level of play which could be achieved by a player who is "freely-available" to any major-league team. The term, which was first coined by Bill James, comes from the concept that a player who plays at "Replacement Level" or below, can be easily replaced by a cheap minor-leaguer or journeyman major-leaguer.

Run Probability Matrix- A matrix indicating the probability of scoring X runs within an inning given the current base-out state. The calculation of a run probability matrix is described here.

Run-Scoring Environment- Average runs scored per game for a particular set of games. Run-scoring environments can vary by ballpark (Coors v. Petco), because of differences in rules (DH v. pitchers hitting), or because of differences across seasons (1968 v. 2000). Run-scoring environment can also be affected by the level of play (little league v. major-league, etc.), although this latter factor is irrelevant to the work presented on this website which deals exclusively with Major-League Baseball.

Standard Deviation- Statistical measure of the spread of a range or distribution. Standard deviation is equal to the square root of the variance. In a normal distribution, approximately 65% of all values will fall within one standard deviation of the mean, 95% of all values will fall within two standard deviations, and 99% of all values will fall within three standard deviations of the mean.

Teammate Adjustments- Effect of a player's teammates on his won-lost record based on shared responsibilities for certain plays between batters and baserunners and/or between pitchers and fielders. Teammate adjustments are described in more detail here.

Three True Outcomes- Strikeouts, walks (or hit-by-pitch), and home runs. These are the only outcomes of a plate appearance that involve only the pitcher and the batter.

Variance- Statistical measure of the spread of a range or distribution. Variance measures the average squared difference of a set of numbers from their mean.

WAR- Wins above Replacement. Measure of total player value developed by Sean Smith, available at Baseball Reference. An alternate measure also called WAR is also calculated by Fangraphs.

WARP- Wins above Replacement Player. Measure of total player value developed by Baseball Prospectus.

Weighted Correlation- Measure of correlation, weighted by the relative size of the individual observations of the sample being measured. The precise calculation of weighted correlation is described here.

Weighted Standard Deviation- Measure of standard deviation, weighted by the relative size of the individual observations of the sample being measured. The precise calculation of weighted standard deviation is described here.

Weighted Variance- Measure of variance, weighted by the relative size of the individual observations of the sample being measured. The precise calculation of weighted variation is described here.

Win Adjustment- Increase in a team's probability of victory relative to the average increase in win probability of a particular event.

Win Probability Matrix- A matrix indicating the probability of a team winning a game given a the current base-out state, the current lead/deficit, and the current inning. The calculation of Win Probability Matrices is described here.

Win Probability- A concept whereby the probability of a team winning a baseball game is estimated based on the current inning, baserunners, outs, and score differential.

Win Shares- Estimated wins contributed by a player. The players on a team receive 3 Win Shares per team win and 0 Win Shares per team loss. Win Shares were developed by Bill James and described in his 2002 book of the same name.

Wins- Player decisions which contribute toward a player's team's probability of winning.

WOPA- Wins over Positional Average.

WOPA_b- Batting wins relative to expected batting wins accumulated by non-pitchers.

WOPA_p- Pitching wins relative to expected average pitching wins.

WOPA_r- Baserunning wins relative to expected baserunning wins accumulated by non-pitchers.

WORL- Wins over Replacement Level.

WORL_f- Fielding Wins over Positional Replacement Level.