e>vars_response</code>
and <code>vars_stressor</code> are assumed to equal <code>"Poor"</code>
(event occurs) or <code>"Good"</code> (event does not occur). If those
default levels do not match the levels of the variables in
<code>vars_response</code> and <code>vars_stressor</code>, the levels of
<code>vars_response</code> and <code>vars_stressor</code> must be
explicitly stated using the <code>response_levels</code> and
<code>stressor_levels</code> arguments, respectively. Similar to
<code><a href="../refe