We all want happiness. However, happiness varies greatly from person to person. A study shows that how happy we are depends on many factors. A psychology professor in California led the study. It could help to provide better treatments for people with depression and anxiety. The professor wrote: "We have to understand the sources of happiness to build effective interventions." Her study has been published in a journal.

The professor suggested that happiness comes from external circumstances or internal feelings. She described three models of happiness. The first is "bottom-up". This is based on factors like wealth, jobs and relationships. The second is a "top-down" model. With this, happiness comes from our attitudes towards life. People can control this through meditation or therapy. The final model is one where the bottom-up and top-down models interact.