Let \( \alpha, \beta (\alpha > \beta) \) be the roots of the quadratic equation \( x^{2}-x-4=0 \). If \( P_{n}=\alpha^{n}-\beta^{n}, \ n \in \mathbb{N} \), then \( \dfrac{P_{15}P_{16}-P_{14}P_{16}-P_{15}^{2}+P_{14}P_{15}}{P_{13}P_{14}} \) is equal to __________.
