We're all bad at predicting

What if I came to you and said "I'm an expert predictor! Give me a 24 win range and I can tell you how well every team in the NBA will do?" Let me give you a practical example. I'm a Nuggets fan. Using the expert prediction skill I mentioned above, I will now make the following prediction:

Next season the Nuggets will win between 40 and 64 games!

Useful right? For the last several seasons, wilQ at Weakside Awareness has done a checkin on how analysts do in terms of predictions at the start of the season and how the season plays out. And the way this is typically interpretted is "Wow John Hollinger is great at predictions! He beat Vegas!" But there's a key flaw here. You see, the story isn't Hollinger is good at predictions, it's that everyone is bad!

The metric wilQ uses is standard error. Now, I trust that wilQ knows the math, he's a very sharp analyst. However, I don't buy that everyone else does. A better way to think of standard error is "What's the range of games I need to place all of my predictions?" The way it works is:

I need twice my standard error to properly predict 20 teams. I need four times my standard error to properly predict 29 teams. With that in mind. Let's redo wilQ's chart of how our analysts did.

Analyst Range of games to get 29 teams "right"
John Hollinger 24
Bovada updated 24
Zach Harper 25
ESPN forecast 26
O/U Line 26
Joe Schaller 26
Cantor Gamings 27
predictionmachine 27
Joel Brigham 27
Las Vegas Hilton 27
George J Monroy 28
Bovada early 28
Matt Moore 28
Sportsbook early 29
Robert Eckstut 29
Bobbo 29
David Williams 29
theNBAmodeller 29
Bradford Doolittle 30
DanielM ASPM 30
version “dumb” 30
Darryl Howerton 30
Ed Weiland 30
WoW1 30
AccuScore 31
WoW2 31
TeamRankings Projections (BETA) 32
Kevin Pelton 33
David Hess 33
SCHOENE 33
Royce Young 34
Derek Ayala 37
ESPN The Magazine and Basketball Prospectus 38
Wins in previous season 39
 
Hollinger needs 24 games to forcast teams (the difference between Boston and Miami) This was better than Vegas, which is apparently the gold standard, by three games. This was a full six games better than the best Wages of Wins model, which is what people are focused on.
 
However, as I mentioned, the key is not that any of these models is best. Rather, it's that they all fail! We're relative creatures, so we want to say - look Bovada did better than Schoene! But in this case, that doesn't matter. The range of games you need is so large, the information is meaningless!
 
A book that everyone purports to have read is "The Signal and the Noise" by Nate Silver. A topic Nate brings up is "Unknowable Unknowables" As the name pretty much says, these are things that you don't know and more importantly, can't know. For instance, Steve Nash got injured this season. No one could have known about this ahead of time and yet, it clearly impacted things. George Karl's decision to not play JaVale McGee, despite the fact he got a major contract, was not knowable ahead of time to anyone.
 
When making predictions, we are making assumptions about many things. One of the things we know pretty well is player evaluation. If a player was good last year, they will probably be good this year. However, even this is unexact. Players perform differently as they age. And of course, rookies are notoriously hard to predict. We have a limited number of things we have a firm grasp on. So it's not surprising that we are bad at predictions.

Updating vs. Predicting

What's key about this is to stop using predictions as the end all be all test. Hollinger is another great example. In the middle of the season Hollinger went to the Memphis front office. And the Grizzlies, who are now in the conference finals, made several moves to their teams. Of course, Hollinger could not have known about these to start the season when he made his predictions. And yet, these moves had some influence on the Grizzlies' success. Using the best data at the time and updating our "predictions" as things progress is the right method. And that's why using metrics that have the best combination of

  • Telling us what happened.
  • Being consistent over time.

Are useful. We can use them to guage what is happening and use them to update our analysis about teams. Trying to become "perfect" at predicting just won't happen. Hollinger has "beaten" Vegas three years now. He hasn't improved the range of games he needs to do it though. And, as I mentioned, that range is rather large. The number of moving parts in a season is vast. It's good to give judgements about the state we think teams are in. Being able to accurately guage how they'll do after 82 games when injuries, trades, breakouts, breakdowns, etc. occur though? It's simply not going to happen.

-Dre

 

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