 theta.sd <span class='op'>=</span> <span class='fl'>1</span>,
  difficulty.mean <span class='op'>=</span> <span class='fl'>0</span>,
  difficulty.sd <span class='op'>=</span> <span class='fl'>1</span>,
  group.size <span class='op'>=</span> <span class='cn'>NULL</span>,
  itemtype.size <span class='op'>=</span> <span class='cn'>NULL</span>,
  group.effect <span class='op'>=</span> <span class='fu'><a href='https://rdrr.io/r/base/c.html'>c</a></span><span class='op'>(</span><span class='fl'>0</span>, <span 