If you live in Fresno County you may soon be getting a knock on the door from the CDC.
The Center for Disease Control is conducting a health and nutrition survey.
The goal of the survey is to look for changes and trends in the US population.
Fresno County's contribution isn't only for itself, but other counties just like it.
"I don't believe we have been here before," says Study Manager Janice Eklund.
Four mobile trailers are turning the Fresno Fairgrounds into a sort of research center.
"We visit 15 counties a year all over the country," she says.
Researchers and doctors from the CDC travel with these trailers all over the United States.
"This is our hearing chamber what we do here is gather information on environmental hearing loss," says Eklund.
From hearing and nutrition tests to body density scans it is all done here starting Tuesday.
They use all the information from the exams and look at health trends and changes so as the population ages they can be prepared.
"The CDC looks at trends so if something looks like it is increasing or spiking then the focus would be at that point to educate and provide for the american population," she says.
The survey is invite only.
Residents selected got an invitation in the mail.
Select field researchers hit the streets knocking door to door to inform those Fresno County residents about the survey.
"They are getting exams they can not get elsewhere and we also thank them for their time by paying them an incentive it is up to $125 for adults."
If you get a knock on the door it may be from someone like Crystal Sacher, a field interviewer.
"When I come to just introduce myself follow up with the letter, let them know we are in town and that the process has begun," says Crystal Sacher.
The data from Fresno County is used to represent other counties just like it.
"If they don't participate we lose the data for that person," says Eklund.
The last day for the survey is March 31st, so you could be getting a knock on the door through the end of March.