de-copy-button"><i class="bi"></i></button></pre></div>
<p>Only the training data <code>x</code> and <code>y</code> are used in the model block. The test data <code>y_tilde</code> and test predictors <code>x_tilde</code> appear in only the generated quantities block. Thus the program is not cheating by using the test data during training. Although this model does not do so, it would be fair to use <code>x_tilde</code> in the model block—only the test observations <code>y_tilde</code> are unknown before th