Nearly half of Shanghai residents have never used a condom, according to a survey conducted by the Shanghai Academy of Social Sciences (SASS) in cooperation with Yale University.

The percentage was higher among the 800 migrants from other provinces and cities in a sample of 2,600 respondents aged 18 to 49 years old, according to the survey report released Tuesday.

A large number didn't even know sexual diseases could be transmitted through sex, Zhou Haiwang, deputy director of the Population Department at the SASS, told the Global Times on Wednesday.

Shanghai was chosen as a populous city with a migrant population of 9 million. While no distinct difference in the quality of sexual life was found between residents and migrants, the survey found people with a better education tended to have a better sex life.

Frequency of sex among migrants was much lower than the long-term residents: 28 percent had sex once a month, according to the research.

Twenty-three percent of married respondents are having or have had extramarital sex, the survey found.

"The figure is much lower than we expected," Zhou said. "It shows that Shanghai residents have a stable marital life."

Among married respondents, 3 percent described their sex life as "terrible," with 72 percent saying they had a good sex life.

Research into three generations of people born in the 1960s, 1970s and 1980s found '80s-born adults' average age for first sex was 21, four years earlier than the 1960s-born group. Some 45 percent of young people chose to co-habit before marriage, three times higher than those born in the 1960s.