The standard normal distribution is a normal distribution of standardized values called
z-scores. A z-score is measured in units of the standard deviation. For example, if the
mean of a normal distribution is 5 and the standard deviation is 2, the value 11 is 3 standard
deviations above (or to the right of) the mean. The calculation is:
x
=
μ
+
(
z
)
σ
=
5
+
(
3
)
(
2
)
=
11
x = μ + (z)σ = 5 + (3)(2) = 11
(1)The z-score is 3.
The mean for the standard normal distribution is 0 and the standard deviation is 1. The transformation
z
=
x
-
μ
σ
z=
x
-
μ
σ
produces the distribution
Z
Z~
N
(
0
,
1
)
N(0,1)
.
The value xx comes from a normal distribution with mean μμ and standard deviation σσ.
- Standard Normal Distribution:
A continuous random variable (RV)
X~N(0,1).X~N(0,1). size 12{X "~" N \( 0,1 \) } {}. When X follows the standard normal distribution, it is often noted as
Z~N(0,1)Z~N(0,1) size 12{Z "~" N \( 0,1 \) } {}.
- z-score:
The linear transformation of the form
z=x−μσz=x−μσ size 12{z= { {x-μ} over {σ} } } {}.
If this transformation is applied to any normal distribution
X~N(
μ
,
σ)X~N(
μ
,
σ) ,
the result is the standard normal distribution
Z~N(0,1)Z~N(0,1) size 12{Z "~" N \( 0,1 \) } {}. If this transformation is applied to any specific value
xx size 12{x} {} of the RV with mean
μμ size 12{μ} {} and standard deviation
σσ size 12{σ} {} , the result is called the z-score of
xx size 12{x} {}. Z-scores allow us to compare data that are normally distributed but scaled differently.
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