Received: 17 May 2019
Accepted: 22 September 2019
First Online: 16 October 2019
Ethics approval and consent to participate
: NHANES study protocols were approved by the research ethics review board of the National Center for Health Statistics. Written informed consent was acquired from each participant and obtained from the guardians of participants younger than 18 years of age, and assent was obtained from those aged 12 to 17 years.
: Not applicable.
: The authors declare that they have no competing interests.