An Overview of Plus/Minus Stats

I remember reading in one of the racer.com mailbags that some IndyCar drivers are very good on starts and/or restarts.  The author wasn't specific about which drivers were good on starts and/or restarts, and I want to know which drivers fall into which group.

Fortunately, the series posts lap charts which I can turn into spreadsheets. Although I don't currently have sector time data from races, I can determine how many spots a driver gains or loses during starts and restarts.  This is a driver's plus/minus, and it's a pretty simple statistic: begin with a driver's position on a start or restart, and subtract the driver's position at the end of the start/restart.  This is already being done at other IndyCar sites (like IndyCar Stats), but only for the entire race (starting position - finishing position).

I plan to track plus/minus over the 2015 season.  I have arbitrarily decided that a start or restart will consist of the 2 laps after the start or restart.  For example, laps 1 and 2 make up the start of a race.  If a race restarts on lap 114, the restart consists of laps 114 and 115.  I plan to calculate plus/minus in the following situations:

• Start +/- (abbreviated as S+/-)
• Restart +/- (abbreviated as R+/-)
• Start and Restart +/- (abbreviated as SR+/-)
• Green flag +/- (abbreviated as G+/-)
• Yellow flag +/- (abbreviated as Y+/-)
• Overall +/- (abbreviated as +/-)

Below are explanations of each plus/minus stat.

Start +/-

• Calculation: Driver's qualifying position - same driver's position at end of lap 2
• Uses: Identifies how many positions a driver gains or loses during the first 2 laps of a race.  Starts are typically double file, while restarts are single file.  Some drivers may be better at passing while running in the unique side-by-side formation used at starts than they are during the single file formation used for restarts.
• Cons: None identified yet

Restart +/-

• Calculation: Sum of a driver's positions at beginning of each restart - sum of same driver's positions 2 laps after each restart
• Uses: Identifies how many positions a driver gains or loses during the first 2 laps after all restarts.
• Cons: None identified yet

Start and Restart +/-

• Calculation: Sum of a driver's S+/- and R+/-.
• Uses: Identifies how many positions a drivers gains or loses during the the start and all restarts.
• Cons: None identified yet

Green Flag +/-

• Calculation: Sum of a driver's positions at beginning of each green flag run - sum of same driver's positions at end of each green flag run
• Uses: Identifies drivers who can pass others during green flag conditions.  G+/- excludes yellow flag conditions, where pit stop time (which is out of the driver's control) can play a large roll in positions gained or lost.
• Cons: May not capture the net effect of strategy decisions.  Consider a driver who makes his final pit stop under green while running 5th, stays on the lead lap, and returns to the race in 10th.  If a yellow flag comes out immediately after he returns to the track but before other drivers pit, the driver who has already stopped will take the lead when other cars make their final stops under caution.  The driver's green +/- will be -5 (5 - 10 = -5), even though his/her team made a good strategy decision to pit before other cars.

Yellow Flag +/-

• Calculation: Sum of a driver's positions at beginning of each yellow flag run - sum of same driver's positions at end of each yellow flag run
• Pros: May identify quick pit crews.  Teams often make pit stops while under yellow flags.  Since the cars are all close together when entering the pits, a quick pit stop under yellow is more likely to gain a position(s) for the car.
• Cons: May not capture the net effect of strategy decisions.  Again, consider a driver who makes his final pit stop under green while running 5th, stays on the lead lap, and returns in 10th.  If a yellow flag comes out immediately after he returns to the track but before other drivers pit, the driver who has already stopped will take the lead when other cars make their final stops under caution.  The driver's yellow +/- will be 9 (10 - 1 = 9), even though (s)he really only gained 4 positions (5 - 1 = 4) with the decision to pit before other cars. 

Overall +/-

• Calculation: Start position - finish position
• Pros: Captures net effect of all strategy decisions.
• Cons: May present an overly simplified view of the race.  A driver who starts and finishes 10th but lead 10 laps and completed a few laps while running in 15th had a much more eventful day than a +/- of 0 would indicate.
• Cons: May not be useful for comparing drivers with different average finishes.  A driver who wins a race from pole will have a +/- of 0.  A very slow driver who qualifies last but manages to finish a race will probably have a slightly positive +/- because (s)he will have passed a few cars that retired early from the race.

Over the course of a season, I would expect championship caliber drivers to have a slightly negative +/-.  The 1 or 2 races where the champion has a bad finish (start 5th, finish 20th for a +/- of -15) will outweigh a +/- figure that would otherwise have been slightly positive.

If the best drivers won't have the best +/- numbers, what good is the stat?  +/- may be useful to compare drivers of similar abilities.  If several drivers are competing for the championship, the driver with the better +/- may be more likely to win the championship.

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