Statistically identifying the most popular science fiction books.

jimharris writes: Over at SF Signal I wrote a piece “How Well-Read Are You in Science Fiction?” There are three databases that collect lists of popular science fiction books that try to statistically identify the best books of the genre. Each site offers a combined list that shows which books were cited the most. They use different sets of best-of lists, but their results are often similar. The final lists are, Classics of Science Fiction, Worlds Without End Top Listed, and Premiosylista Comparativas: Comparativas: Ciencia ficción (Spain). Is this a good methodology for identifying the classics of science fiction? What other methodologies could be designed?