Dropout: A Simple Way to Prevent Neural Networks from Overfitting, Nitish Srivastava, Geoffrey Hinton, Alex Krizhevsky, Ilya Sutskever, Ruslan Salakhutdinov, 2014Journal of Machine Learning Research, Vol. 15 - Original academic paper introducing the Dropout regularization technique and providing initial recommendations for its application and dropout rates.
Deep Learning, Ian Goodfellow, Yoshua Bengio, Aaron Courville, 2016 (MIT Press) - A comprehensive textbook that provides a detailed explanation of Dropout as a regularization method and general strategies for hyperparameter selection.