Being sad may actually be a good thing because Australian researchers have found that bad moods make people less gullible, more critical and also boosts memory.

Joseph Forgas, a psychology professor at the University of New South Wales, headed the study that found people in a negative mood showed improved ability to assess others and were more attentive to their surroundings than happier people, who were more likely to believe anything they were told.

"Whereas positive mood seems to promote creativity, flexibility, cooperation, and reliance on mental shortcuts, negative moods trigger more attentive, careful thinking paying greater attention to the external world," the Courier Mail quoted Prof Forgas as saying.

"Our research suggests that sadness ... promotes information processing strategies best suited to dealing with more demanding situations," he added.

The study also found that a "mildly negative mood may actually promote a more concrete, accommodative and ultimately more successful communication style".

"Positive mood is not universally desirable: people in negative mood are less prone to judgmental errors, are more resistant to eyewitness distortions and are better at producing high-quality, effective persuasive messages," Prof Forgas wrote.