Editing WKB approximation (section)

===Probability density===
One can then compute the probability density associated to the approximate wave function. The probability that the quantum particle will be found in the classically forbidden region is small. In the classically allowed region, meanwhile, the  probability the quantum particle will be found in a given interval is approximately the ''fraction of time the classical particle spends in that interval'' over one period of motion.<ref>{{harvnb|Hall|2013}} Conclusion 15.5</ref> Since the classical particle's velocity goes to zero at the turning points, it spends more time near the turning points than in other classically allowed regions. This observation accounts for the peak in the wave function (and its probability density) near the turning points.

Applications of the WKB method to Schrödinger equations with a large variety of potentials and comparison with perturbation methods and path integrals are treated in  Müller-Kirsten.<ref>Harald J.W. Müller-Kirsten, Introduction to Quantum Mechanics: Schrödinger Equation and Path Integral, 2nd ed. (World Scientific, 2012).</ref>