Imagine with me if you will:

You're an NBA GM.  You have a pick in the draft.  Your team needs a SG and some help in the front line, so a PF.  You want to pick someone who would be a starter sooner rather than later.  What position would be the safest pick?

If you chose a F, you would be more likely to have selected a bust.  

***Note:  While Greg Oden is a clear bust, in my counting, I also chose players like 2001 #9 Rodney White who bounced around but never stuck, or 1999 #5 Jonathan Bender who played for a while but never really started or had quality minutes, or 1993 #8 Vin Baker who played in an All Star game but wasn't ever really worth the value that he was drafted at or paid.***

I tallied all the drafts from 1984-2008 (some of the later drafts haven't solidified 'bust' status yet so I only counted those that fit my scheme in the 05-08 draft).  I only looked at the top 15 picks.  In my opinion a Top 15 pick should be a player that makes a significant contribution on the court immediately ('89 #14 Tim Hardaway), develops into a solid role playing starter ('94 #10 Eddie Jones), has star power ('96 #15 Steve Nash), or has longevity providing a role for a team ('95 #10 Kurt Thomas).  If you're drafted in the Top 15 and you don't do any of those things, to me, you're a bust.

Below is my count.

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Based on these counts you're over twice as likely to draft a bust by drafting a forward than you are to draft a guard or center.