Researchers want to know how Downtown residents are faring, mentally and physically, 10 years after the Sept. 11 attacks. Beginning this month they will be knocking on doors to try to find out.

The person-to-person outreach is part of an effort to boost resident participation in the World Trade Center Health Registry’s current survey, the third so far.

Among the other groups being surveyed, area workers and people involved in the recovery, residents have the lowest response rate.

About 41 percent of residents en­rolled in the registry had responded by mid-December. A little over half of recovery workers and general workers have answered the survey.

“We want to hear from everyone, because we want to get the full picture,” said Mark Farfel, director of the World Trade Center Health Registry. “Every survey counts.”

For the survey to be accurate, Farfel stressed that it is important for all participants to respond—whether or not they believe they are still feeling the effects of living near the destruction.

About 14,000 of the estimated 71,000 people who were living below Canal Street in 2001 are enrolled in the registry.

In past surveys, Farfel said, about one in five enrollees reported symptoms of post-traumatic stress disorder in the last five years; one in 10 enrollees had asthma. (Specific numbers for residents were not included in data provided to the Trib.) Health impacts varied according to the amount of exposure to dust.

Farfel hopes the current survey will allow researchers to get a look at the persistence of certain conditions and to check for any new health problems that may have arisen for participants since the last survey in 2006.

The current survey has an expanded mental health section. In addition to screening for signs of post-traumatic stress disorder, the new survey also asks about depression and anxiety, as well as sleeping habits and drug use, Farfel said.

“For the adults as well as the children, we really put more emphasis on mental health,” Farfel said. “We definitely want to take a look at the course of PTSD, but we also want to look more closely at depression and anxiety. And they often go together.”

The findings from past research have helped influence public policy, including the passage by Congress of the James Zadroga 9/11 Health and Compensation Act of 2010.

Researchers will begin analyzing data after the survey ends in March, and Farfel said he expects findings to be published the following year.