Module 6

Statistics

Sample Size

  • Descriptive Statistics – discussed in Module 1, characterize data, dispersion, central tendency (baseball analytics)
  • Inferential Statistics – use a sample of the population and draw inferences about the whole population (projections)
  • Law of Large Numbers – as sample size goes up, the sample estimate gets closer to the population estimate
  • Calculating sample size is more of a statistical focus than this course.  Factors are z score, standard deviation of the population, and margin of error
    • If z score goes up, sample size goes up
    • If SD goes up, sample size goes up
    • If margin of error goes up, sample size goes down
  • Russell Carleton (pizzacutter) study in 2007 todetermine how long baseball stats take to normalize (stay consistent with each other)
    • Plotted Batting Average in odd at bats vs. Batting Average in even at bats
    • Wanted R^2 of at least 0.50

Sabermetrics

WAR

  • Wins Above Replacement
  • Statistical framework for total offense and defense contributions that reflects performance and playing time
  • Variations
    • WARP (Baseball Prospectus)
    • fWAR (fangraphs)
    • bWAR / rWAR (Baseball Reference)
    • oWAR (Open source WAR)
  • Components:
    • Replacement level
    • Runs to Wins
    • Runs Estimators
  • Morris Greenberg has studied the three main variations of WAR
    • Cannot predict any WAR measure just by knowing another alternative WAR calculation
    • The three variations do not have a relationship to each other
    • The three methods are probably assigning different values of wins for hitter production
    • Increased playing time leads to a greater variance between the three measures (amplifies the differences)
    • Hitters who play 2B, SS, CF have more variant outcomes than other positions, meaning these positions have different variations in fielding calculations
    • There are also more variation for pitchers in the extremes (the top and the bottom pitchers).  Probably due to how the systems attribute pitcher outcomes to pitchers versus defense.
  • Basis framework of calculating WAR is to use the pythagorean calculations and extending out the calculation to become:  W/L = (R/RA)^2
  • Instead of squaring this calculation, you can try todetermine the best exponent to use (instead of 2)
    • For 1901 to current, the best fit exponent is 1.863

Technology

  • Park Factor = 100 * ((homeRS+homeRA)/homeG) / ((roadRS+roadRA)/roadG)
  • Anything over 100 is above average, below 100 is below average
  • Can use this same formula for any batting statistic
  • This SQL query on the retrosheet game log can help you calculate it for teams (this one is doing a HR park factor)ParkFactorSQL

R Studio

  • lm() – fitting linear models
  • function(arglist) expr
    return(value)
  • Build functions to create automated method of recalculating things you would commonly like to reperform

SQL

  • CASE
    WHEN (expression)
    ELSE
    END

History

George Lindsey

  • Canadian, University of Toronto, WWII, PhD from Cambridge, Nuclear Scientist
  • First work, in 1959, was a look at batting average and if it could be used to predict future performance.
    • Concludes there were too many variables at play (differing pitchers, parks, situations, leagues, etc.).
    • Conducted a study of same-sided batter-pitcher matchups and found a statistically significant result that an advantage exists for opposite handed hitters
    • First published statistical study of L/R batting splits
    • Also first published look at run scoring expectancy in bases loaded situations
    • Was trying to figure out if you should try for a force out at home in bases loaded situations or if you should try for a double play
  • 2nd paper, Progress of the Score During a Baseball Game
    • Isthe probability of scoring in any half inning the same?  Is run scoring by inning homogeneous?
      • 1st (high), 2nd (low), 3rd (high) are different from mean
      • Likely due to structure of batting order
    • Does the history of scoring affectsubsequent innings?  Is scoring independent?
      • Large run scoring seems to not be independent
      • Lead changes follow a model of independence, meaning there is no tendency to overcome leads
    • Studied home field advantage (54%)
  • 3rd paper, An Investigation of Strategies in Baseball
    • Tries to address steal a base or not to, sacrifice bunt with less than 2 outs, IBB when 1st base is open, etc.
    • The most important runs (in terms of affecting win probability) are those that tie the score or put you 1 run ahead
    • Analyzed all base states and the probability of scoring 0, 1, 2 runs.  Also looked at the expected runs for each situation.
    • He uses these expectations to determine optimal strategy (if you bunt in this situation, what does it do to your expected runs?).
    • If you are in a specific situation and then you hit a triple, what happens?  What happens to your expected runs in the new situation?  How much does it increase from before?
    • The beginning of linear weights
    • A value added approach of measuring a player
    • Concludes IBB is not useful except for winning by one run and runners on 2 and 3 (the likelihood of scoring 0 runs increases by actually loading the bases, but the overall expected run value of this goes up too)
    • Concludes to always play double play depth with a runner on 1st, except with a runner on third that would tie the game/take the lead
    • Concludes sacrifice play does not improve scoring chances.
    • Concludes stolen bases value is dependent upon an individual’s success rate

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