The S&P 100 CDS Index initially comprises 80 to 90 members of the S&P 100 that have CDS's with sufficient liquidity. The weight of each constituent in the index is based upon its weight in the S&P 100. There is no minimum ratings criteria, although most reference entities are investment grade.
The US Investment Grade Index comprises 100 equally-weighted investment grade US corporate credits which meet certain liquidity criteria. The US High Yield Index comprises 80 equally-weighted high yield US