.. note::
    :class: sphx-glr-download-link-note

    Click :ref:`here <sphx_glr_download_packages_scikit-learn_auto_examples_plot_measuring_performance.py>` to download the full example code
.. rst-class:: sphx-glr-example-title

.. _sphx_glr_packages_scikit-learn_auto_examples_plot_measuring_performance.py:


Measuring Decision Tree performance
====================================

Demonstrates overfit when testing on train set.


Get the data



.. code-block:: python


    from sklearn.datasets import load_boston
    data = load_boston()







Train and test a model



.. code-block:: python

    from sklearn.tree import DecisionTreeRegressor
    clf = DecisionTreeRegressor().fit(data.data, data.target)

    predicted = clf.predict(data.data)
    expected = data.target







Plot predicted as a function of expected



.. code-block:: python


    from matplotlib import pyplot as plt
    plt.figure(figsize=(4, 3))
    plt.scatter(expected, predicted)
    plt.plot([0, 50], [0, 50], '--k')
    plt.axis('tight')
    plt.xlabel('True price ($1000s)')
    plt.ylabel('Predicted price ($1000s)')
    plt.tight_layout()




.. image:: /packages/scikit-learn/auto_examples/images/sphx_glr_plot_measuring_performance_001.png
    :class: sphx-glr-single-img




Pretty much no errors!

This is too good to be true: we are testing the model on the train
data, which is not a mesure of generalization.

**The results are not valid**


**Total running time of the script:** ( 0 minutes  0.062 seconds)


.. _sphx_glr_download_packages_scikit-learn_auto_examples_plot_measuring_performance.py:


.. only :: html

 .. container:: sphx-glr-footer
    :class: sphx-glr-footer-example



  .. container:: sphx-glr-download

     :download:`Download Python source code: plot_measuring_performance.py <plot_measuring_performance.py>`



  .. container:: sphx-glr-download

     :download:`Download Jupyter notebook: plot_measuring_performance.ipynb <plot_measuring_performance.ipynb>`


.. only:: html

 .. rst-class:: sphx-glr-signature

    `Gallery generated by Sphinx-Gallery <https://sphinx-gallery.readthedocs.io>`_