z alpha by 2 distribution-help!

How do we use z aplha by 2 distribution? I don't get it one bit. For the table it says z on lhs and second decimal place of z on the top in the rhs. Firstly if e.g apha is 0.05 then apha by 2 is 0.025 so we know that we have z subscript 0.025 so how on earth do we use the table if we know only the value of alpha and not the value of z, what on earth do we look for in the tables?

Original post by gn17

How do we use z aplha by 2 distribution? I don't get it one bit. For the table it says z on lhs and second decimal place of z on the top in the rhs. Firstly if e.g apha is 0.05 then apha by 2 is 0.025 so we know that we have z subscript 0.025 so how on earth do we use the table if we know only the value of alpha and not the value of z, what on earth do we look for in the tables?

I'm not clear why you're doing alpha/2, but setting that aside:

Since the tables only have data for alpha to 2 decimal places you need to use linear interpolation.

So, look up z(0.02) and z(0.03), then

Z(0.025)\approx [Z(0.02) + Zz(0.03)]/2

Reply 2

BananaPie

I'm guessing you're probably using alpha/2 in situations like confidence intervals or something. But for 0.025 and any other decimal <0.5 you can just look at the table and find what value of Z corresponds with the value of the decimal. If you look at 0.025 you should see it corresponds with 1.96

z alpha by 2 distribution-help!

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