What is a projection?

When I was growing up an astrologist named Jeane Dixon was famous because she had predicted that President John F. Kennedy would be assassinated before he actually was. She was a popular author and newspaper columnist who regularly published her predictions of what was to come and many people bought them. For a time I bought them, even though every rational bone in me said there was no evidence that she knew more about what was to come than I did. Jeane Dixon’s secret was to aggressively promote her hits and quickly forget about the predictions that didn’t come true. Her perfidy was easy to see, yet for her readers the potential power that would come from knowing what was to come before it came was overwhelmingly attractive. I couldn’t help my curiousity.

Just a little foreknowledge can make a huge difference in many fields. For instance, IT departments in financial trading companies are doing everything they can to analyze data a little faster and then get their trades done before their competitors can. Hundredths of a second can be the difference between winning and losing a trade, and winning has a cascade effect. More better trades gives a trader the ability to use increased resources to leverage an even bigger advantage (maybe by speeding up the computers and communication equipment another few hundredths of a second).

POP CULTURE ASIDE: In T-Bone Burnett’s song “The Strange Case of Frank Cash and the Morning Paper” a down-on-his-luck horseplayer discovers that his sports section has yesterday’s horse results but next week’s football scores. He soon climbs out of the financial hole he’s in and gets famously wealthy, moves into a new house, and can hardly wait for the next football season to begin. But when his new maid brings him the paper the new season’s scores are last week’s. He realizes that it was the paper at his old flophouse that was magic, and then things get strange. It turns out the “magic” was in the way Burnett spun the story about a gambler with a sure thing, and by the end of the song Frank Cash’s son is destined, thanks to the storyteller, to be president of the United States, of all things. It’s one crazy song.

When we think of the ideal player projections we usually imagine numbers similar to Frank Cash’s football scores. Perfect numbers. If we know Adam Dunn isn’t going to hit 40 homers before the start of the 2011 season, we’ll have a huge advantage over our opponents, we think. And if we know he is going to hit 40 homers before the start of the 2012 season, we’ll gain a similar advantage. If you know he’s going to hit 11 homers one year, and 42 the next, you’ve struck gold. So, perfect projections are the Platonic ideal to which we all aspire, right?

Well, sure, that would be nice. These pieces about stat projections explain why that isn’t possible in any sense, and what you can expect with projections and why that can be valuable, too.

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