Question

Why is the standard normal curve sometimes referred to as the z-curve?

Short answer

In the standard normal curve, a dummy variable $z-$has been used. So, it referred to as the z-curve.

Step-by-step solution

Concept Introduction

In conventional normal distributions, a normal curve is known as the normal random variable, such as a $z-$score.

The following equation can be used to convert any normal random variable $X$into a$z$score:

$Z=\frac{(X-\mu )}{\sigma }$

Explanation 

We refer to the $z$scores on the horizontal axis of the standard normal curve as $z$scores since the standard normal curve represents a normally distributed variable.

This shows that the $z-$curve is sometimes indicated as standard normal curve.