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Bicho the Inhaler · Daedalian Member

I can't remember my statistics training! Suppose I take two samples, consisting say of N1 and N2 individuals, and I find that M1 individuals of the N1 sample have property Q, and M2 individuals of the N2 sample have property Q. How do I determine if the difference between the two samples is significant? Is this the t-test? I don't remember exactly how to do this type of test; when the results are valid; etc.

Thanks in advance.

Ghost Post · Icarian Member

no, it's a two sample z test
p=proportion with Q

z= p1-p2
sqrt(p_pooled(1-p_pooled)(1/n1+1/n2))

Ghost Post · Icarian Member

you look up the Z value you get on a table to see the probability of result that or more extreme. You need to decide in advance how small the probability should be to be significant, usually 5% or 1%.

Bicho the Inhaler · Daedalian Member

Ha ha, that looks vaguely familiar. Thanks, RSA.

Ghost Post · Icarian Member

no problem, the stats ap is fast approaching so this stuff is at the forefront of the ol' mind

Legion · Daedalian Member

Yeah, also Excel does t-test, p-test, a-test for you! But you gotta know haow to drive the thing.