Every day, through Facebook status updates, people share how they feel with those who matter most in their lives. These updates are tiny windows into how people are doing. They're brief, to the point, and descriptive of what's going on this week, today or right now.

Grouped together, these updates are indicative of how we are collectively feeling. At Facebook, we're always looking for ways to help people better understand the world around them, and we're interested in how people express their emotions with one other and the world. So earlier this year, data scientists at Facebook started a project to measure the overall mood of people from the United States on Facebook, based on the sentiment expressed in status updates.

The result was an index that measures how happy people on Facebook are from day-to-day by looking at the number of positive and negative words they're using when updating their status. When people in their status updates use more positive words—or fewer negative words—then that day as a whole is counted as happier than usual.

Though more countries or languages may be added later, the current result is notable since it is based on the updates of all English-speaking U.S. Facebook users. In this sense, it can count as an indicator of "Gross National Happiness," a metric only measured currently via Gallup polls and national surveys in countries such as France and Bhutan. To protect your privacy, no one at Facebook actually reads the status updates in the process of doing this research; instead, our computers do the word counting after all personally identifiable information has been removed.

For our Gross National Happiness index, we adapted a collection of positive and negative emotion words built by social psychologists. Examples of positive or happy words include "happy," "yay" and "awesome," while negative, or unhappy words, include "sad," "doubt" and "tragic." We also did a brief survey of some Facebook users, which showed that people who use more positive words, relative to the number of negative words, reported higher satisfaction with their lives.

Over time, we've seen spikes in the index for different days of the year. Some of the happiest days include U.S. national holidays like Thanksgiving and Fourth of July, social holidays like Halloween and religious holidays including Christmas and Easter. Wednesday, Nov. 5, 2008—when the U.S. was celebrating the election of President Barack Obama—was over twice as happy as the average Wednesday.