weights
if not NULL, weights to use in computing the estimate. this
should be the name of the column in the survey.data which
has the variable with the appropriate weights. these weights
should be construted so that, eg, the mean of the degrees
is estimated as (1/n) * \sum_i w_i * d_i
known.popns
if not NULL, a vector whose entries are the
size of the known
populations, and whose names are the variable names in the dataset
corresponding to each one. if NULL, then assume that the survey.data
dataframe has an attribute called 'known.popns' containing this vector.