S&P 500 use "close" or "adjusted close"

[coolio]

I'm trying to compare my portfolio to the S&P 500. When figuring % increases, do you use the "close" figure or the "adjusted close" for that day? I'm looking at Google Finance where I'm getting these S&P figures.

I'm thinking the adjusted close includes dividends for all the companies that are part of the S&P, but I'm not sure. Can someone set me straight?