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S1 normal distribution

how are you meant to now if you are meant to do 1- phi(z)

the normal case is when the value of z= -... then you have to do 1-phi(z)
but when the value of z= +.... , when do you do 1- phi(z)

any help would be appreciated thanks :biggrin:

Reply 1

claret_n_blue

If you have standardised/normalised your data, then it is now in terms of 'x' and you are now working out say

P(Z < z) = phi(z).

Correctly, you said P(Z < -z) = phi(-z) = 1 - phi(z).

Also, if you wanted to do P(Z > z) then you would also do 1 - P(Z < z) = 1 - phi(z).

Why? If you look at your graph of the standard Normal distribution, because it is symmetric, you get that these two values are the same.