Glade, N.; Ballet, P.; Bastien, O. (2012). “A stochastic process approach of the drake equation parameters”. 《International Journal of Astrobiology》 11 (2): 103–108. arXiv:1112.1506. Bibcode:2012IJAsB..11..103G. doi:10.1017/S1473550411000413. S2CID119250730. Note: This reference has a table of 1961 values, claimed to be taken from Drake & Sobel, but these differ from the book.
Glade, N.; Ballet, P.; Bastien, O. (2012). “A stochastic process approach of the drake equation parameters”. 《International Journal of Astrobiology》 11 (2): 103–108. arXiv:1112.1506. Bibcode:2012IJAsB..11..103G. doi:10.1017/S1473550411000413. S2CID119250730. Note: This reference has a table of 1961 values, claimed to be taken from Drake & Sobel, but these differ from the book.
"The value of N remains highly uncertain. Even if we had a perfect knowledge of the first two terms in the equation, there are still five remaining terms, each of which could be uncertain by factors of 1,000." from Wilson, TL (2001). “The search for extraterrestrial intelligence”. 《Nature》 (Nature Publishing Group) 409 (6823): 1110–1114. Bibcode:2001Natur.409.1110W. doi:10.1038/35059235. PMID11234025. S2CID205014501., or more informally, "The Drake Equation can have any value from "billions and billions" to zero", Michael Crichton, as quoted in Douglas A. Vakoch; 외. (2015). 《The Drake Equation: Estimating the prevalence of extraterrestrial life through the ages》. Cambridge University Press. ISBN978-1-10-707365-4., p. 13
Golden, Leslie M. (2021) “A joint mind consideration of the Drake equation in the search for extraterrestrial intelligence,” Acta Astronautica, 185, 333-336; https://doi.org/10.1016/j.actaastro.2021.03.020
Glade, N.; Ballet, P.; Bastien, O. (2012). “A stochastic process approach of the drake equation parameters”. 《International Journal of Astrobiology》 11 (2): 103–108. arXiv:1112.1506. Bibcode:2012IJAsB..11..103G. doi:10.1017/S1473550411000413. S2CID119250730. Note: This reference has a table of 1961 values, claimed to be taken from Drake & Sobel, but these differ from the book.
"The value of N remains highly uncertain. Even if we had a perfect knowledge of the first two terms in the equation, there are still five remaining terms, each of which could be uncertain by factors of 1,000." from Wilson, TL (2001). “The search for extraterrestrial intelligence”. 《Nature》 (Nature Publishing Group) 409 (6823): 1110–1114. Bibcode:2001Natur.409.1110W. doi:10.1038/35059235. PMID11234025. S2CID205014501., or more informally, "The Drake Equation can have any value from "billions and billions" to zero", Michael Crichton, as quoted in Douglas A. Vakoch; 외. (2015). 《The Drake Equation: Estimating the prevalence of extraterrestrial life through the ages》. Cambridge University Press. ISBN978-1-10-707365-4., p. 13
Brin, G. D. (1983). “The Great Silence – The Controversy Concerning Extraterrestrial Intelligent Life”. 《Quarterly Journal of the Royal Astronomical Society》 24 (3): 283–309. Bibcode:1983QJRAS..24..283B.
"The value of N remains highly uncertain. Even if we had a perfect knowledge of the first two terms in the equation, there are still five remaining terms, each of which could be uncertain by factors of 1,000." from Wilson, TL (2001). “The search for extraterrestrial intelligence”. 《Nature》 (Nature Publishing Group) 409 (6823): 1110–1114. Bibcode:2001Natur.409.1110W. doi:10.1038/35059235. PMID11234025. S2CID205014501., or more informally, "The Drake Equation can have any value from "billions and billions" to zero", Michael Crichton, as quoted in Douglas A. Vakoch; 외. (2015). 《The Drake Equation: Estimating the prevalence of extraterrestrial life through the ages》. Cambridge University Press. ISBN978-1-10-707365-4., p. 13
Glade, N.; Ballet, P.; Bastien, O. (2012). “A stochastic process approach of the drake equation parameters”. 《International Journal of Astrobiology》 11 (2): 103–108. arXiv:1112.1506. Bibcode:2012IJAsB..11..103G. doi:10.1017/S1473550411000413. S2CID119250730. Note: This reference has a table of 1961 values, claimed to be taken from Drake & Sobel, but these differ from the book.
"The value of N remains highly uncertain. Even if we had a perfect knowledge of the first two terms in the equation, there are still five remaining terms, each of which could be uncertain by factors of 1,000." from Wilson, TL (2001). “The search for extraterrestrial intelligence”. 《Nature》 (Nature Publishing Group) 409 (6823): 1110–1114. Bibcode:2001Natur.409.1110W. doi:10.1038/35059235. PMID11234025. S2CID205014501., or more informally, "The Drake Equation can have any value from "billions and billions" to zero", Michael Crichton, as quoted in Douglas A. Vakoch; 외. (2015). 《The Drake Equation: Estimating the prevalence of extraterrestrial life through the ages》. Cambridge University Press. ISBN978-1-10-707365-4., p. 13