Detecting Outliers

[ErwinO]

I'm new to this Forum and bought recently "Excel Simulations" from Dr. G.M. Verschuuren.

In Chapter '73. Detecting Outliers' I struggle with formula =NORMINV(RAND(),30,15)*(1-2*RAND()). It centers values around Zero and excluding '-2*RAND()' it centers around the average of 30.

Is it a kind of Linear Transformation?

Maybe you could help?

Erwin

 

[pgc01]

... I struggle with formula =NORMINV(RAND(),30,15)*(1-2*RAND()). It centers values around Zero and excluding '-2*RAND()' it centers around the average of 30.

Hi Erwin
Welcome to the board

It's not excluding '-2*RAND()', it's excluding "*(1-2*RAND())"

1-2*RAND() has an average of 0

NORMINV(RAND(),30,15) has an average of 30

This means that you are multiplying 2 independent random variables, one that has an average of 30 and another one that has an average of 0.

If I remember correctly from school, the average of the product of two independent random variables is equal to the product of their corresponding averages.

You'd expect in this case an total average of 0.

 

[ErwinO]

thanks, I have to Digest.

Erwin

 

[pgc01]

You're welcome. Thanks for the feedback.

... I have to Digest. ...

Maybe while drinking a herbal tea?