I'm reading Forensics: A Guide for Writers by D. P. Lyle. When the author talks about the probabilities of forensic testing results, he says:
'No two people have the same DNA, but the testifying expert will not say that the DNA “absolutely matches” that of the defendant. Instead he will say that the probability that it matches is a billion to one. That is almost, but not quite, absolute.'
'The probability that the theory holds true could be 50 percent (coin toss), 90 percent (probable), 99.999 percent (highly probable), or 50 million to 1 (virtually 100 percent probable).'
Does "a billion to one" mean "one in a billion" and "50 million to 1" mean "1 in 50 million"? I thought both phrases mean that something is extremely unlikely. But the context of the above two paragraphs seems to suggest that the two phrases mean that something is extremely likely.
Now I'm confused. Do they mean something is likely or unlikely? Can anybody explain the idea for me?