Owing to the fact that a Living Reviews in Relativity article may evolve over time, we recommend to cite the article as follows:
Misao Sasaki and Hideyuki Tagoshi,
"Analytic Black Hole Perturbation Approach to Gravitational Radiation",
Living Rev. Relativity 6, (2003), 6. URL (accessed <date>):
The date given as <date> then uniquely identifies the version of the article you are referring to.