The basic finding:
The return correlation between Facebook and Zinga is greater that the correlation between Facebook and the S&P 500 and the trading volume correlation between FB and the S&P 500 is greater than the volume correlation between FB and Zinga.
I thought I'd run the numbers - here's what I got:
|ann SD (i)||
|Correl of volume||0.2592||1.0000||0.3256|
|R-sqr from CPM||
Obviously these are two stocks that have very low market risk - less that 1% of their returns is explained by the S&P 500. ZNGA has a negative beta, and the confidence interval for both betas is huge.
In other words, these are two stocks whose risk is virtually all idiosyncratic. It is probably a mistake to put any weight on these beta estimates.