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 May 18th, 2009, 09:19 AM #1 Newbie   Joined: May 2009 Posts: 1 Thanks: 0 How to regress actual data towards projected data. Hey all, So I am currently working on a system that will predict the outcome of MLB games. I need a method to regress a player's actual stats with his predicted stats. By the end of the season, I want player A's predicted stats for a single game to be 50% projections 50% actual. For example, let's say player A is projected to play 50 games and hit at an average of .300. In actuality, player A has played 25 games and is hitting .200. So what can we predict player A's average to be for his 26th game? Originally I went with a formula like this w = weight = Games played actual/Games played predicted = .5 Average(26th game) = (Projected Average)*(1-(w/2)) + (Actual Average)*(w/2) Average(26th game) = (.300)*(.75) + (.200)*(.25) = .275 This looks all well and good, but things start getting messy if we let the actual games played get larger than 2x the predicted. For example... Average(201st game) = (.300)*(1-(4/2))+(.200*(4/2)) Average(201st game) = -.300 + .400 = .100 Now obviously this result is not correct. In this scenario, a players predicted average for a single game should NEVER drop below his actual average for the entire season. Instead, as the actual games played approaches infinity, the predicted average for a single game should approach the actual average. I'm not sure how to calculate this. May 18th, 2009, 10:01 AM #2 Global Moderator   Joined: Nov 2006 From: UTC -5 Posts: 16,046 Thanks: 938 Math Focus: Number theory, computational mathematics, combinatorics, FOM, symbolic logic, TCS, algorithms Re: How to regress actual data towards projected data. You're weighting the actual games as ((actual games)/(predicted games))/2 but it seems that you should weight them as (actual games)/(predicted games + actual games). This would probably solve your issue. Tags actual, data, projected, regress Thread Tools Show Printable Version Email this Page Display Modes Linear Mode Switch to Hybrid Mode Switch to Threaded Mode Similar Threads Thread Thread Starter Forum Replies Last Post lumpa Real Analysis 0 October 19th, 2012 08:07 AM gaz Algebra 4 November 24th, 2010 11:11 PM minicoop503 Algebra 1 September 8th, 2009 03:06 PM ramyy Applied Math 1 June 29th, 2009 04:49 PM EddSjd Algebra 2 September 8th, 2007 10:06 AM

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