A latest University of California, San Diego, study has found that emotions can be contagious even in the virtual online world. The researchers found that positive posts/updates led to more optimistic reactions and negative posts triggered more pessimistic ones. However, positive posts were more influential or infectious.

"Our study suggests that people are not just choosing other people like themselves to associate with but actually causing their friends' emotional expressions to change," lead author James Fowler, professor of political science in the Division of Social Sciences and of medical genetics in the School of Medicine at UC San Diego, said in a statement. "We have enough power in this data set to show that emotional expressions spread online and also that positive expressions spread more than negative."

This is the first study to focus on emotional contamination in online social networks.

For the study, the researchers examined anonymous Facebook status updates in the U.S. between January 2009 and March 2012. They did not look at the names or the user's words mentioned in the posts.

The emotional content of each post was measured through a software program called the Linguistic Inquiry Word Count (LIWC) that consists of a default set of words. When it analyzes a text, it correlates a word to a particular emotion.

In the study, the researchers focused on rain-related facebook updates and found that number of negative posts increased by 1.16 percent, while the positive ones fell by 1.19 percent.

The researchers further looked at posts of people who were friends with someone in other cities where it wasn't raining. Each positive post triggered 1.75 more positive posts among friends; while each negative post produced 1.29 more negative ones.

"To get away from measuring the effect of the rain itself, we had to exclude the effects of posts on friends who live in the same cities. But we have a pretty good sense from other studies that people who live near each other have stronger relationships and influence each other even more. If we could measure those relationships, we would probably find even more contagion," Fowler said.

The finding is published in the journal Plos One.