@Unpublished{Riv07b,
  author = 	 { Ronald L. Rivest },
  title = 	 { A Simple Rule of Thumb for Election Audit Size Determination },
  note = 	 { Unpublished draft. },
  date =         { 2007-10-31 },                  
  OPTyear = 	 { 2007 },
  OPTmonth = 	 { October 31, },
  abstract =     {
         This note proposes a very simple ``Rule of Thumb'' for
         determining how many precincts to audit in a post-election audit. 
         This rule says to audit $1/m$
         precincts (rounded up to the next integer), where $m$ is
         the ``margin of victory'' (the difference in percentage
         of votes for the apparent winner and for the apparent
         runner-up). For example, if the margin of victory is
         4\%, then this rule of thumb suggests auditing 
         $ 1.0/0.04 = 25$ precincts. If the formula suggests auditing more
         precincts than are available, all precincts are audited.
         \par
         This Rule of Thumb gives a guaranteed ``confidence
         level'' of at least 92\% when certain assumptions hold
         (when all precincts have the same size and the miscount
         within each precinct is at most 20\% of the votes in that
         precinct). Under these assumptions, the actual confidence
         level achieved ranges from 92\% to 100\%.
         \par                  
         This Rule of Thumb is simple enough to be computed
         in one's head; it provides reasonable guidance for 
         ``back-of-the-envelope'' estimates, and is useful 
         when the simplicity of the formula is especially important.                  
        },
}