a quivver or arrows, page-6

I have a question regarding iindex participation.

What is the criteria to be added or removed from different indexes.
Eg. I was look at CXY and CNX and these are the ones CNX are in where CXY arent in any.

Also what affect does it have on a stock when added or removed.

Here is what cnx is in

Index Participation
Index Name Weight
All Ordinaries 0.02%
S&P/ASX 300 0.02%
S&P/ASX 300 Energy (Industry Group) 0.23%
S&P/ASX 300 INDUSTRIALS 0.02%
S&P/ASX 300 RESOURCES 0.06%
S&P/ASX SMALL ORDINARIES 0.20%
S&P/ASX SMALL RESOURCES 0.60%