Bangkok residents are the most unhappy in the country, and the national sentiment has slumped, according to the latest survey on gross domestic happiness.

Out of a possible 10 points, Bangkok residents' happiness was rated at just 5.54 in a survey conducted by the Abac Poll Research Centre between August 25 and September 12.

The survey - of 4,864 people in 25 provinces - focused on their happiness last month.

The most happy people in the country were those living in Northeast, where the gross happiness index touched 6.69 points.

"Since we have conducted the gross domestic happiness surveys, the Northeast has always emerged as the happiest region," the research centre's director Noppadon Kannika said yesterday.

He said the country's happiness slipped to just 6.34 points last month from 7.29 in July.

In June, when the country celebrated the 60th anniversary of His Majesty King Bhumibol Adulyadej's accession to the throne, the index soared to 9.21 points.

Noppadon said respondents were still most happy about Thai culture and their loyalty to the monarchy. People's family ties, health, job satisfaction and good relationships with others in the same community also contributed.

According to the survey, a higher income does not mean more happiness. When divided into groups based on incomes, 19 per cent of those earning less than Bt5,000 a month said they were happy while only 9 per cent of those earning more than Bt30,000 a month said they were happy.

"It should also be noted that those who strictly embrace [the King's] sufficiency-economy theory recorded a higher gross happiness index," Noppadon said.

He said all parties should formulate clear policies on how to increase the happiness index instead of just focusing on developments driven by capitalism.