Being unemployed, out of the workforce or working part-time when wanting to work full-time are the strongest predictors of having depression, according to a new study by Gallup.

The US-based research group found that the depression rate was highest among those not in the workforce (16.6%) and unemployed (11.4%).

Those who were employed part-time when they wanted to work full-time had the third highest depression rate (10.6%).

By contrast, employed and self-employed people had a far lower depression rate (5.6% and 5.1%).

Similarly, those who were working part-time and did not want to work full-time had a lower depression rate of 7.6%. 

"It is possible that there is something about employment contributes to lower depression rates, or it could be that those who have depression are less able to seek out and retain employment," Gallup said.

The findings are based on surveys of more than 100,000 Americans conducted between January 1 and July 25 this year.

The survey asked participants whether they had ever been diagnosed with depression and whether they are currently suffering from the condition.

Overall, 10% of respondents said they had been diagnosed with and currently had depression.

In addition to employment, people earning below $36,000 (around £23,000) are also more likely to suffer from depression. Women were also twice as likely as men to say they had depression, at 13.2% compared to 6.5%.

Those aged 18 to 21, or over the age of 65, and black or Hispanic people were less likely to have depression.

Depression peaked among 57 to 64-year-olds at just over 14%, compared to the rate of just 5.4% among 18 to 21-year-olds. However, by the age of 76, the depression rate dropped to 8.6%.

Gallup said: "While one in 10 Americans currently have depression, this analysis shows that certain segments of the population are more likely to suffer from the illness than others.

"Americans who are unemployed, underemployed, and not in the workforce are more likely to report having depression than those who are employed full time or who are content with being employed part time.

"Thus, the stubborn unemployment and underemployment rates may have more than just a negative impact on the nation's economic recovery, they also may present a significant threat to Americans' mental health and wellbeing."