A recent study has found that people with lower IQs are more likely to have lower income and poor mental health, which is in turn linked with unhappiness.

The study examined data from the 2007 Adult Psychiatric Morbidity Survey in England. All of the participants were 16 years old or older, and all lived in private residences. Thus, people in prisons or in other taxpayer-funded homes were excluded from the study. Verbal IQs were obtained from participants' performance on the National Adult Reading Test. In addition, categorical and continuous IQs were used.

Happiness was measured by analyzing answers based on a three-point question. One such question was "Taking all things together, how would you say you were these days - very happy, fairly happy, or not too happy?"

The happiest IQ group was people who scored between 120 and 129 on the exam, with 43 percent of the highest group reporting that they were very happy. The least happy IQ group was the lowest group, which scored between 70 and 99. They had the highest proportion of people say that they were not too happy, at 12 percent.

The study found that, in addition to lower income and poor mental health, people with lower IQs were more likely to suffer from poor overall health and to need help with daily life, like grocery shopping and housework. All of these factors were likely to contribute to general unhappiness.

Researchers believe that there should more help available for people with low IQs. "There is some evidence that long term intensive strategies directed at young children from socially deprived backgrounds can have a positive impact not only on IQ, but also on wellbeing and life opportunities," Dr. Angela Hassiotis, one of the authors of the study, said. "Such interventions are likely to be costly, but the initial costs may be offset by future benefits such as a reduced reliance on state benefits and better mental and physical health."

A score of 129 is considered above average on an IQ test. A score of 70 is considered to be borderline intellectual functioning. Scores between 85 and 114 are considered average on an IQ test.

IQ tests have been considered controversial because many argue that they are not accurate representations of overall intelligence, but rather a certain type of intelligence. Many say that various factors, like genes and environment, can influence scores. Others say that the tests contain bias.

The study was published in a recent issue of Psychological Science.