The codebook is returned as a list object. Returns NULL upon error.
Arguments
nh_table
The name of the NHANES table that contains the desired variable.
colname
The name of the table column (variable).
dxa
If TRUE then the 2005-2006 DXA codebook will be used (default=FALSE).
Details
Each NHANES variable has a codebook that provides a basic
description as well as the distribution or range of values. This
function returns the full codebook information for the selected
variable. If the environment variable NHANES_TABLE_BASE
was set during startup, the value of this variable is used as the
base URL instead of https://wwwn.cdc.gov (this allows the
use of a local or alternative mirror of the CDC documentation).