Equivalence of script lines
Message/Author
 Jas Wer posted on Monday, August 24, 2015 - 5:15 am
Hi,

My question is about using a script shortcut.

I'm using a bivariate Cholesky decomposition to examine genetic and environmental influences on the association between two variables. I would like to express the genetic and environmental influences on each variable as a proportion of the total variance, which entails dividing the genetic or environmental influence by the total variance for that variable.

The genetic influence on Variable1 is defined as
a11=x11**2;
and the total variance on variable 1 as
v11 = x11**2 + y11**2 + z11**2;

So now, for obtaining genetic influences as a proportion of total variance, I'm using this line:

h1=x11**2/(x11**2 + y11**2 + z11**2);

However, I was wondering whether I could also just write it it like this:

h1=a11/v11;

Is there any reason why one should use the first version over the second? It does make quite a big difference in the time it takes to run the models and in the length of the script lines.

Also, related to this: what exactly does the double asterisk mean, anyway? I couldn't find this in the User's Guide.

Thanks and best wishes
 Bengt O. Muthen posted on Tuesday, August 25, 2015 - 7:27 am
You can write it either way and it makes no difference.

Double asterisk means "to the power of 2".