The notation for the chi-square distribution is:
χ
2
χ
2
~
χ
df
2
χ
df
2
where
df
=
df= degrees of freedom depend on how chi-square is being used. (If you want to
practice calculating chi-square probabilities then use
df
=
n
-
1
df=n-1. The degrees of freedom
for the three major uses are each calculated differently.)
For the
χ
2
χ
2
distribution, the population mean is
μ
=
df
μ=df and the population
standard deviation is
σ
=
2
⋅
df
σ=
2
⋅
df
.
The random variable is shown as
χ
2
χ
2
but may be any upper case letter.
The random variable for a chi-square distribution with
k
k degrees of freedom is the
sum of
k
k independent, squared standard normal variables.
χ
2
=
(
Z
1
)
2
+
(
Z
2
)
2
+
...
+
(
Z
k
)
2
χ
2
=(
Z
1
)
2
+(
Z
2
)
2
+...+(
Z
k
)
2
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