title: How to take into account missing data in Kappa coefficient calculation?
body: <p>I am calculating an inter-rater agreement for a biological question.
  Basicaly, 6 readers are evaluated on 60 subjects with 2 possibilities categorical scale for each subjects.
  I am using kappam.fleiss function on R to do so.</p>
  <p>My question is: how to take into account missing data ?
  If I put &quot;NA&quot; on my database, I am scared that NA would be interpreted as a new entry for the categorical interpretation. and thus would be associated with an abnormal kappa value.</p>
  <p>Thanks a lot.</p>
  <p>Thomas</p>