Reference:

Javier Esparza, Antonín Kučera, and Richard Mayr. Quantitative analysis of probabilistic pushdown automata: Expectations and variances. In LICS 2005, pages 117–126. IEEE Computer Society, 2005.

Suggested BibTeX entry:

@inproceedings{EKM05,
    author = {Javier Esparza and Anton\'{\i}n Ku\v{c}era and Richard Mayr},
    booktitle = {LICS 2005},
    pages = {117--126},
    publisher = {IEEE Computer Society},
    title = {Quantitative Analysis of Probabilistic Pushdown Automata: Expectations and Variances},
    year = {2005}
}