S1 Help - Simple Questions on Variance...

HI!
Just need some help!

Does Sxx = Variance of X ?
Syy = Variance of Y?

Sigma(xi^2) - (Sigma xi)^2 / n = Sxx....

What happened to the mean there? Is Sigma (xi^2) the mean? But it dun have a /2 under it?? Ehh?

Thanks for any help :smile:

Reply 1

makesomenoise

I think you mean E, not sigma. E stands for expectation or expected value.

Reply 2

Buzfvar

It is definitely sigma, straight from the formula book for Edexcel, you know.

Reply 3

makesomenoise

Buzfvar

It is definitely sigma, straight from the formula book for Edexcel, you know.

Oh OK. Just had a look at my AQA formula book. This is to do with correlation, not variance.

Reply 4

kikzen

Buzfvar

Σ is the sign for 'sum'. I cant really remember S1 that well, but this looks like PMCC (Product Moment Somethign Correlation).

You had to work out these things to get something else :s-smilie:

Not very helpful eh.

But at least you know its not the mean :smile:

E(X) is the mean.

Reply 5

makesomenoise

kikzen

Σ is the sign for 'sum'. I cant really remember S1 that well, but this looks like PMCC (Product Moment Somethign Correlation).

You had to work out these things to get something else :s-smilie:

Not very helpful eh.

But at least you know its not the mean :smile:

E(X) is the mean.

Product moment correlation coefficient, just so you know. :smile:

Reply 6

Buzfvar

Yep, the formula is used for correlation...

Reply 7

kikzen

XTinaA

Product moment correlation coefficient, just so you know. :smile:

hehe yeh thats what i meant :smile:

Reply 8

nooneknows

Sxx and Sxy (and Syy) are values used in the calculation of the PMCC and linear regression lines - I don't think they have anything to do with variance (they're definitely not related to it in S1).

They're pretty useless one there own....check the graphic for the associated formulae.