Confusing Z Scores In Normal Distributions

[Gabe Rebs]

Hello, Good Day! I just want to understand or someone could explain to me why are there different versions of Z scores. I couldnt tell the difference between them and I am kind of in a Panic on What to Use. I saw one version where its positive and One is negative, then there is also this version where theres no positive or negative. How do I use them accordingly?

 

[Dr.Peterson]

Hello, Good Day! I just want to understand or someone could explain to me why are there different versions of Z scores. I couldnt tell the difference between them and I am kind of in a Panic on What to Use. I saw one version where its positive and One is negative, then there is also this version where theres no positive or negative. How do I use them accordingly?

They aren't different Z scores; they give two different areas (from -infinity, and from the mean). Your first two tables give areas from -infinity to z, for negative and positive values of z, respectively; the last gives areas from 0 to z. Most tables I've seen include at least a picture to explain what area is shown.

What are you trying to use it for?