Op 25-06-10 15:41, Michiel Van Bel schreef:
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.
So if we take numbers we can imagine, say 20 blue pencils, 2 red ones... we should get the same chance that those two red ones are lying next to each other as the chance they're not? I never was too good at statistics either...
*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 :-(
-- ================================================================== Thomas Van Parys Tel:+32 (0)9 331 36 95 fax:+32 (0)9 3313809 VIB Department of Plant Systems Biology, Ghent University Technologiepark 927, 9052 Gent, BELGIUM thomas.vanparys@psb.vib-ugent.be http://bioinformatics.psb.ugent.be ==================================================================