Michiel Van Bel wrote:
Elisabeth Wischnitzki wrote:
Michiel Van Bel wrote:
Michiel Van Bel wrote:
Frederik Delaere wrote:
Michiel Van Bel wrote:
okay, my statistics is a bit rusty (and I do not really know how to google for it), so perhaps you guys might have a hint:
1) say you have X objects (in a linear row) 2) Y of those X objects (Y <= X naturally) have some kind of special status 3) Z is a number between 0 and Y 4) What are the odds that Z objects with the special status are located next to each other
For example: X=50,Y=20,Z=10 You have 50 pencils, and 20 of them are red, 30 of them are blue. What are the odds that (if you lay those 50 pencils down randomly) there are 10 red pencils next to each other?
Anyone any hints?
ask in the forums on unibet.com ?
okay, if I follow Marijn's reasoning: I get that the chance is approx. (N-Z) * (Y!) / ((N-Z)!) This should be great, except for the fact of course that N and Y are pretty big numbers (N : 30000 genes, Y : 10 to 10000 GO terms), and Z is pretty small (10 or so). 30000! is a rather largish number actually :-/
Okay, Elisabeth came up with a very good remark: the chance that 10 red pencils are next to each other, is the same as any other random combination of red and blue pencils. ...
*grmbl* And with numbers as big as these, it is indeed probably better to just take the background frequency Y/X Although it still doesn't really "feel" right to me... but that is always the case with statistics
see this for example: http://en.wikipedia.org/wiki/Monty_Hall_problem Still makes no real sense to me :-(
Btw: (N-Z)! is not 50*49*48...etc it is you example 40*39*...*2*1
N! / (N-Z)! is what you are looking for..
But...there is no Y in that formula! *starts weeping silently under his desk*
Screw it, I'll create my own statistic theories, with blackjack and hookers. In fact, forget about the statistics!
just for the last part..and you also don't want to place all your Y red pencils but just 10. So the whole thing would be: (N-Z) * (Y! / (Y-Z)!) / (N! / (N-Z)!) -- ================================================================== Elisabeth Wischnitzki Tel:+32 (0)9 331 38 22 fax:+32 (0)9 3313809 VIB Department of Plant Systems Biology, Ghent University Technologiepark 927, 9052 Gent, BELGIUM elwis@psb.vib-ugent.be http://www.psb.vib-ugent.be ==================================================================