IDS 702 In-class analysis 5

Predicting nba wins I

Due: 1 hour after class ends

Housekeeping

Structure and format

You will work in your pre-assigned teams. Each team should submit ONLY ONE report for this exercise. You must write the names of all team members at the top of the report containing your responses. You all must do the work using one student’s computer and R/RStudio.

Have one team member open R/RStudio on their computer and share their screen with the other team members within the breakout room. At the top of the team report, write “host” in parenthesis besides this student’s name. Have another team member be responsible for documenting the responses. At the top of the team report, write “writer” in parenthesis besides this student’s name.

NOTE: Generally, you will not be penalized for not taking on these roles many times during the semester. This is to simply ensure that you do switch the roles around a “decent number” of times within each team throughout the semester. That said, I will penalize any student who obviously dominates these roles over everyone else, so be sure to give other students an opportunity to do them.

R/RStudio

You all should have R and RStudio installed on your computers by now. If you do not, first install the latest version of R here: https://cran.rstudio.com (remember to select the right installer for your operating system). Next, install the latest version of RStudio here: https://www.rstudio.com/products/rstudio/download/. Scroll down to the “Installers for Supported Platforms” section and find the right installer for your operating system.

Gradescope

Gradescope will let you select your team mates when submitting, so make sure to do so. Only one person needs to submit the sheet on Gradescope. You can submit your document in the most common formats, but pdf files are preferred. Submit on Gradescope here: https://www.gradescope.com/courses/280392/assignments. Be sure to submit under the right assignment entry.

Introduction

The purpose of this exercise is to give you additional practice working with logistic regression. The exercise is based on the NBA Team Game Stats dataset found here: https://www.kaggle.com/ionaskel/nba-games-stats-from-2014-to-2018/. Read more about the problem and dataset under the description section of the link.

Kaggle is a great online community of data scientists. To learn more about Kaggle, follow this link: https://www.kaggle.com/getting-started/44916.

For this exercise, you will need to select ONLY ONE NBA team in the data. Also, you will need to set aside data for the 2017/2018 season as test data. Write the name of the team you selected at the top of your report

The data

Download the data (named nba_games_stats.csv) from Sakai and save it locally to the same directory as your R markdown file. To find the data file on Sakai, go to Resources \(\rightarrow\) Datasets \(\rightarrow\) In-Class Analyses. Once you have downloaded the data file into the SAME folder as your R markdown file, load and clean the data by using the following R code.

Again, you are expected to select ONLY ONE NBA team in the data. Also, set aside data for the 2017/2018 season as test data.

nba <- read.csv("nba_games_stats.csv",header = TRUE,sep = ",",stringsAsFactors = FALSE)

# Set factor variables
nba$Home <- factor(nba$Home)
nba$Team <- factor(nba$Team)
nba$WINorLOSS <- factor(nba$WINorLOSS)

# Convert date to the right format
nba$Date <- as.Date(nba$Date, "%Y-%m-%d")

# Also create a binary variable from WINorLOSS. 
# This is not always necessary but can be useful 
#particularly for R functions that prefer numeric binary variables
#to the original factor variables
nba$Win <- rep(0,nrow(nba))
nba$Win[nba$WINorLOSS=="W"] <- 1

# I picked the Charlotte Hornets (CHO) as an example,
#you should pick any team you want
nba_reduced <- nba[nba$Team == "CHO", ]

# Set aside the 2017/2018 season as your test data
nba_reduced_train <- nba_reduced[nba_reduced$Date < "2017-10-01",]
nba_reduced_test <- nba_reduced[nba_reduced$Date >= "2017-10-01",]

You will only use the nba_reduced_train data today, but will use the nba_reduced_test data in the next in-class exercise.

Code book

Variable Description
Team Abbreviation for the name of the team
Game Game index for the season. Each team plays 82 games per season
Date Date of the game
Home Home or away game?
Opponent Abbreviation for the name of the opposing team
WinorLoss Did the team win? W = win, L = loss
Win Binary re-coding of WinorLoss. 1 = win, 0 = loss
TeamPoints Number of total points scored in the game
OpponentPoints Number of total points scored by the opposing team in the game
FieldGoals Number of field goals made in the game (also includes 3 point shots but not free throws)
FieldGoalsAttempted Number of field goals attempted in the game (also includes 3 point shots but not free throws)
FieldGoals. FieldGoals/FieldGoalsAttempted
X3PointShots Number of 3 point shots made in the game
X3PointShotsAttempted Number of 3 point shots attempted in the game
X3PointShots. X3PointShots/X3PointShotsAttempted
FreeThrows Number of free throws made in the game
FreeThrowsAttempted Number of free throws attempted in the game
FreeThrows. FreeThrows/FreeThrowsAttempted
OffRebounds Number of offensive rebounds grabbed in the game
TotalRebounds Total number of rebounds grabbed in the game (includes OffRebounds)
Assists Total number of assists (passes leading to a made field goal) in the game
Steals Total number of steals (balls stolen from the opposing team while the opposing team has possession) in the game
Blocks Total number of blocks (direct prevention of a made field goal after the ball has been shot by an opposing player) in the game
Turnovers Total number of times the ball was lost back to the opposing team while the team had possession.
TotalFouls Total number of fouls committed on players on the opposing team
Opp.FieldGoals Number of field goals made by the opposing team in the game (also includes 3 point shots but not free throws)
Opp.FieldGoalsAttempted Number of field goals attempted by the opposing team in the game (also includes 3 point shots but not free throws)
Opp.FieldGoals. Opp.FieldGoals/Opp.FieldGoalsAttempted
Opp.X3PointShots Number of 3 point shots made by the opposing team in the game
Opp.X3PointShotsAttempted Number of 3 point shots attempted by the opposing team in the game
Opp.X3PointShots. Opp.X3PointShots/Opp.X3PointShotsAttempted
Opp.FreeThrows Number of free throws made by the opposing team in the game
Opp.FreeThrowsAttempted Number of free throws attempted by the opposing team in the game
Opp.FreeThrows. Opp.FreeThrows/Opp.FreeThrowsAttempted
Opp.OffRebounds Number of offensive rebounds grabbed by the opposing team in the game
Opp.TotalRebounds Total number of rebounds grabbed by the opposing team in the game (includes Opp.OffRebounds)
Opp.Assists Total number of assists (passes leading to a made field goal) by the opposing team in the game
Opp.Steals Total number of steals (balls stolen from the team while the team has possession) by the opposing team in the game
Opp.Blocks Total number of blocks (direct prevention of a made field goal after the ball has been shot by a player on the team) by the opposing team in the game
Opp.Turnovers Total number of times the ball was won back from the opposing team while the opposing team had possession.
Opp.TotalFouls Total number of fouls committed by players on the opposing team

Team abbreviations and acronyms

Abbreviation/
Acronym
Franchise
ATL Atlanta Hawks
BOS Boston Celtics
BRK Brooklyn Nets
CHO Charlotte Hornets
CHI Chicago Bulls
CLE Cleveland Cavaliers
DAL Dallas Mavericks
DEN Denver Nuggets
DET Detroit Pistons
GSW Golden State Warriors
HOU Houston Rockets
IND Indiana Pacers
LAC Los Angeles Clippers
LAL Los Angeles Lakers
MEM Memphis Grizzlies
MIA Miami Heat
MIL Milwaukee Bucks
MIN Minnesota Timberwolves
NOP New Orleans Pelicans
NYK New York Knicks
OKC Oklahoma City Thunder
ORL Orlando Magic
PHI Philadelphia 76ers
PHO Phoenix Suns
POR Portland Trail Blazers
SAC Sacramento Kings
SAS San Antonio Spurs
TOR Toronto Raptors
UTA Utah Jazz
WAS Washington Wizards

Exercises

Treat the variable Win (or WinorLoss) as your response variable and the other variables as potential predictors. Answer all questions using only the nba_reduced_train data. Leave the `nba_reduced_test data for next time.

  1. Make exploratory plots to explore the relationships between Win and the following variables: Home, TeamPoints, FieldGoals., Assists, Steals, Blocks and Turnovers. Don’t include any of the plots, just briefly describe the relationships.

  2. Just by looking at the code book, there are several combinations of variables we should not include as predictors in the logistic model. Identify at least two pairs and explain in at most two sentences, why we should not include them in the model at the same time.

  3. Fit a logistic regression model for Win (or WinorLoss) using Home, TeamPoints, FieldGoals., Assists, Steals, Blocks and Turnovers. as your predictors. Using the vif function, are there are any concerns regarding multicollinearity in this model?

  4. Present the output of the fitted model and interpret the significant coefficients in terms of the odds of your team winning an NBA game.

  5. Using 0.5 as your cutoff for predicting wins or losses (1 vs 0) from the predicted probabilities, what is the accuracy of this model? Plot the roc curve for the fitted model. What is the AUC value?

Acknowledgement

This exercise is based on ideas proposed by Sam Voisin.