# What is I . sG2 / m?

**URL:** <https://isgw-forum.colorado.edu/t/what-is-i-sg2-m/353>\
**Category:** Day 7\
**Created:** [June 15, 2022, 11:02am UTC](https://isgw-forum.colorado.edu/t/what-is-i-sg2-m/353 "2022-06-15T11:02:36Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![x.mo](https://isgw-forum.colorado.edu/letter_avatar_proxy/v4/letter/x/a4c791/32.png) [@x.mo](https://isgw-forum.colorado.edu/u/x.mo)\
**Post date:** [June 15, 2022, 11:02am UTC](https://isgw-forum.colorado.edu/t/what-is-i-sg2-m/353/1 "2022-06-15T11:02:36Z")

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In the record of “From correlation coefficients to variance components”, slide 15.  
it was mentioned that in the model, Y = X b + e ; b follows a normal distribution of N(0, I . sG2 / m ).  
I want to know what is I, S and G2?

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**Author:** ![baptiste.CD](https://isgw-forum.colorado.edu/letter_avatar_proxy/v4/letter/b/8491ac/32.png) [@baptiste.CD](https://isgw-forum.colorado.edu/u/baptiste.CD)\
**Post date:** [June 15, 2022, 3:39pm UTC](https://isgw-forum.colorado.edu/t/what-is-i-sg2-m/353/2 "2022-06-15T15:39:09Z")

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Good question, the notation I used could be clearer.  
I is the identity matrix (a NxN matrix with 1 on the diagonal and 0 otherwise), sG2 is a number and corresponds to the variance of the random effect (square of the standard deviation). In several papers it is called sigma\_G squared, which is more self explanatory but I got a bit lazy typing the equations.