Figure 1.
Flow diagram of the process of enrollment of 3,473 never-smoker subjects in the fourth Korean National Health and Nutrition Examination Survey (KNHANES).
Abbreviation: PFT, pulmonary function test.
Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.