Written by Makram Talih in 2019.
df_method: for "default", df = degf(design); for "NHIS", df = nrow(design) - 1.
To use this adjustment in surveytable tabulations, call set_survey() or set_opts() with the
mode = "NCHS" argument, or type: options(surveytable.adjust_svyciprop = TRUE).
NHIS users, be sure to set the surveytable.adjust_svyciprop.df_method option to
"NHIS".