Fascinating (and compelling) methodology that has demonstrated to be valid - that you can detect the likelihood of contracting a contagious outbreak of an epidemic by monitoring the health of your friends.
Dr. James Fowler, Professor of Medical Genetics & Political Science at University of California (San Diego) proposed that people who have more friends will tend to become infected by contagions sooner than others with fewer friends. See Social Network Sensors for Early Detection of Contagious Outbreaks.
To test the method, Dr. Fowler and his team recently studied an H1N1 flu epidemic at Harvard College. Results showed that by simply monitoring the friends of randomly selected individuals, two weeks of advanced notice could have been given for this particular outbreak. Thus, monitoring friends is a good way to alert oneself at being at risk - better than checking your own symptoms.