1)

I don't understand the meaning of the last line. When is X random? When is X fixed? Can anyone illustrate each case with a quick example?

β

ε

note: also under discussion in "Math Help Forum" & "SOS math cyberboard"

**"In regression models, there are two types of variables:**

X = independent variable

Y = dependent variable

Y is modeled as random.

X is sometimes modeled asX = independent variable

Y = dependent variable

Y is modeled as random.

X is sometimes modeled as

*random*and sometimes it has*fixed*value for each observation."I don't understand the meaning of the last line. When is X random? When is X fixed? Can anyone illustrate each case with a quick example?

β

ε

note: also under discussion in "Math Help Forum" & "SOS math cyberboard"

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