l with some constraints</span></span>
<span><span class="va">lavmodel</span> <span class="op">&lt;-</span> <span class="st">"</span></span>
<span><span class="st">      O=~ O3+O8+O13+a*O18+a*O23+1.2*O28</span></span>
<span><span class="st">      O ~ 1   # estimate mean</span></span>
<span><span class="st">      O ~~ O  # estimate variance</span></span>
<span><span class="st">      # some constraints among thresholds</span></span>
<span><span class="st">      O3  | d1*t1</span></span>
<span><span class="st">