If <span class="math inline">\(\theta\)</span> is the true value and <span class="math inline">\(\hat{\theta}\)</span> the estimate, then error is just the difference between the prediction and the true value, <span class="math display">\[
\textrm{err} = \hat{\theta} - \theta.
\]</span></p>
<p>If the estimate is larger than the true value, the error is positive, and if it’s smaller, then error is negative. If an estimator’s unbiased, then expected error is zero. So typically, absolute error or squared e