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.
Eh?! The clue is, ofcourse, that the 10 pencils can be luying at any given spot of the 50 free positions. I think you need to calculate it like that. First calculate all possibilities of 10 spots next to eachother. Assume these 30 are red. Then fill all other spots with the remaining pencils. Now you only have to calculate somehow the overlap between the solutions. Eg. First 10 are red and last 10 are red, that configuration will be counted twice. I dunno. Sofie
...
*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 :-(
-- Sofie Van Landeghem PhD Student VIB Department of Plant Systems Biology, Ghent University Bioinformatics and Evolutionary Genomics Technologiepark 927, 9052 Gent, BELGIUM Tel: +32 (0)9 331 36 95 fax:+32 (0)9 3313809 Website: http://bioinformatics.psb.ugent.be