inc
either a numeric vector giving the
(equivalized disposable) income, or (if data is
not NULL) a character string, an integer or a
logical vector specifying the corresponding column of
data.
weights
optional; either a numeric vector giving
the personal sample weights, or (if data is not
NULL) a character string, an integer or a logical
vector specifying the corresponding column of
data.
years
optional; either a numeric vector giving the
different years of the survey, or (if data is not
NULL) a character string, an integer or a logical
vector specifying the corresponding column of
data. If sup