Java Script Issue: auto populate "Yes or No" Value.

I am trying to create a java script to auto populate a yes or no value in one field based on a value in another field. I tried the following script, but it did not work:

if(Depth To Water ft2 <= 20.20) {     Submerged YN2 = "Yes"; } else {     Submerged YN2 = "No"; }