# Thread: Help! Z is annoying!

1. ## Help! Z is annoying!

Hi, I need help with understanding z.

People always talk about z tests- but what does z actually mean? Is it the null?

I've been given examples like P(Z>0.5) and you work out a value from that (the value in the book says 0.3085). I found that value on one table, which was a one tailed normal distribution function, and for another question, P(Z<0.7) found the answer to be 0.7580 in another version of essentially the same table. But this table starts at 0.5000- it doesn't go down as far a 0.3085 so I'm really confused, how could two tables that should be the same be THAT different??

Also, how do you read the tables properly? What does the top bar (0.00, 0.01, 0.02...) and the bottom bar (0.0, 0.1, 0.2.....) actually stand for?

I've got an exam on friday so please help- the lecturer can't explain anything- always 1 word answers!

Thanks!

2. ## mistake

Originally Posted by 10rob11
Hi, I need help with understanding z.

People always talk about z tests- but what does z actually mean? Is it the null?

I've been given examples like P(Z>0.5) and you work out a value from that (the value in the book says 0.3085). I found that value on one table, which was a one tailed normal distribution function, and for another question, P(Z<0.7) found the answer to be 0.7580 in another version of essentially the same table. But this table starts at 0.5000- it doesn't go down as far a 0.3085 so I'm really confused, how could two tables that should be the same be THAT different??

Also, how do you read the tables properly? What does the top bar (0.00, 0.01, 0.02...) and the bottom bar (0.0, 0.1, 0.2.....) actually stand for?

I've got an exam on friday so please help- the lecturer can't explain anything- always 1 word answers!

Thanks!
p.s. I didn't mean bottom bar, I meant the one on the side.

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