[R] Simplify formula for heterogeneity

[Stefaan Lhermitte]

Thank you very much Ted! I have been looking at your simplification for 
more then an hour, but I don't see how you did it.
Could you perhaps, if it is not to much work, explain me how you reduced 
H? It would help me to understand what I am realy doing.

Looking at the result, it seems indeed that H does add more information 
than sd already did. Intuitively I thought the square of the sum of all 
possible differences would not be related to the standard deviation. 
Looking at your result it seems it is related by a factor sqrt(2*(n-1)) 
so there is no special point in calculating  H and I know I cannot trust 
my intuition anymore.

Thanks again!

Kind regards,
Stef