dframe</code>.  The default value is <code>NULL</code>.</p></dd>


<dt>fpc</dt>
<dd><p>Object that specifies values required for calculation of the
  finite population correction factor used during variance estimation. The
  object must match the survey design in terms of stratification and whether
  the design is single-stage or two-stage.  For an unstratified design, the
  object is a vector.  The vector is composed of a single numeric value for a
  single-stage design.  For a two-stage unstratified desig