Diversification is hard to find nowadays because financial markets are becoming increasingly correlated. I found a good visually presentation of Cross Sectional Correlation of stocks in the S&P 500 index in the Trading correlation by D. Varadi and C. Rittenhouse article. Let’s compute and plot the average correlation among stocks in the S&P 500 index 








Zero Inflated Models and Generalized Linear Mixed Models with R.
Zuur, Saveliev, Ieno (2012).