Fowler and Christakis (2008) report that personal happiness tends to be associated with having a social network including many other happy friends. To test this claim, a researcher obtains data from a sample of 84 people asking them how happy they are, and then asking them to identify the number of close friends whom they consider to be happy people.

Is this:

1. Experimental

2. Correlation

3. Non-Experimental

4. Quasi-Experimental