a</dt>
<dd><p>A <code>bysg</code> or <code>byperson</code> data set in wide format with the variable <code>sg_session_n</code> and all variables specified in <code>extract_var_list</code>.</p></dd>


<dt>id_var_name</dt>
<dd><p>String, specifying the name of the ID variable.</p></dd>


<dt>extract_var_list</dt>
<dd><p>List or vector, specifying the variable names of session to session scores to extract from.
If this is a list, the name of each element will be used when creating new variables.
Note that each