prop</th>
      <td><p>Variance of the proportional error component</p></td>
    </tr>
    <tr>
      <th>var_add</th>
      <td><p>Variance of the additive error component</p></td>
    </tr>
    </table>

    <h2 class="hasAnchor" id="value"><a class="anchor" href="#value"></a>Value</h2>

    <p>A building block of type 'observation'</p>
    <h2 class="hasAnchor" id="details"><a class="anchor" href="#details"></a>Details</h2>

    <p>Observation models specify the observed variable, how an observation is
e