Basic (or maybe not) Z-Score Math Question

jaybarg  3/5/2014 9:53 AM

Hi,

I have a question related to the interpretation of the Z-Scores:

Consider the scenario where I know the final player Z-Scores for a season, in this case 2013.  If I could make a trade that would take effect at the start of the 2013 season, is it valid to add the Z-Score of all the players involved to determine fairness?

Is this a valid use of Z-Score or not?

Thanks!

Metsox  3/5/2014 10:03 AM

I asked a similar question vis a vis whether to trade the second round pick in the draft for the seventh pick and a fourth rounder. 

It depends on your league but in order for you to "win" that trade you would need to pick up a 0 value player off the waiver wire. And generally in a deep league it's impossible to do that. The best guy off the waiver wire might rate at -.50. 

You have to field 2 players and you have to deduct the cost of having a crappy second player from Kershaw's goodness. 

So I would definitely rather have McCutchen and Beltre. But like you I am not sure I am thinking about it correctly.

silentjim   3/5/2014 10:05 AM

Depends on a few things like are you using per game stats or total stats.

Using z scores for uneven trades whether averaging or totaling or not is also difficult because there's always the question of who is the replacement player filling in this case Adrian Beltre's shoes?

If you're looking at the Miggy side, it's based on last seasons numbers, can you find a replacement player who will get you 82 runs, 39 RBI, 7 HR, 24 SBs, and all at a decent average since this is the difference between McCutchen and Beltre minus Miggy's stats are to fit that now open roster spot.

There's some other things to weigh as well like positional value and other players on your team etc.

silentjim   3/5/2014 10:07 AM

Obviously use the trade analysis feature too if you haven't already, which you're already technically doing.

ken_admin  3/5/2014 10:20 AM

Adding z-scores does not give accurate results for all categories. For instance, if you have three hitters with these batting average z-scores, 0.00 0.00 +1.5, adding them gives +1.5 though it should be closer to +0.05 in reality. This happens with any ratio category: avg, ERA, WHIP, etc. Pure stat categories like home runs are pretty close when adding.

liam4  3/5/2014 10:25 AM

I agree with all the posts below.

That said, I happen to add z-scores just like you spoke about though, as a rule of thumb, in most leagues.  But I'm a very active waiver wire/trade player and want top stars, and assume I can find a player with 0.0 value to replace the second, or may have them on my bench. I also look to "Win" the trade with a higher z-score.  This may not be applicable in deep or very experienced leagues.  But getting Cabrera... priceless.

jaybarg  3/5/2014 10:30 AM

A lot of replies and quickly!

@MetSox: Yes, someone emailed me this point exactly.  Makes total sense.

@silentjim: I used total stats. The assumption was that I made this trade at the start of the year and held those players until the end.  Also get the point about positional value + team context however I wanted to get this straight before I started adding complications

@kslight: If I get your point a better approach with the McC +  Beltre side would be to add the Z-Scores for the counting stats (HR, RBI, etc..), but take the average Z-Score for batting average to formulate a combined Z-Score for that side of the trade.

All your feedback is greatly appreciated.