In Blade Runner, Deckard says that it takes 20-30 questions to identify a replicant (and a hundred for Rachel).
However, when I saw the movie yesterday, I realised that even after the first question or two it becomes blindingly obvious that the respondents think and act like machines ("I'd kill it!").
The only explanation I can come up with why it then would take dozens of questions, would be that the human population has gone cynical from the apocalypse and all come off as non-empathic.
I can't remember the detail at which the novel describes the Voight-Kampff test, but the logical flaw could possibly have been introduced during the screenwriting process.
Any other explanations or comments?