One in a billion
Discussion
davepoth said:
Simple probability based on the number of base pairs I would guess. One in a billion still means there are seven people in the world who would match that sample...
In which case the chance of it not being from Stephen Lawrence is 6 in 7, not 1 in a billion. That's why I can't understand what can possibly give rise to the one in a billion figure.Dr Jekyll said:
davepoth said:
Simple probability based on the number of base pairs I would guess. One in a billion still means there are seven people in the world who would match that sample...
In which case the chance of it not being from Stephen Lawrence is 6 in 7, not 1 in a billion. That's why I can't understand what can possibly give rise to the one in a billion figure.ATG said:
Dr Jekyll said:
davepoth said:
Simple probability based on the number of base pairs I would guess. One in a billion still means there are seven people in the world who would match that sample...
In which case the chance of it not being from Stephen Lawrence is 6 in 7, not 1 in a billion. That's why I can't understand what can possibly give rise to the one in a billion figure.If there are 7 people in the world matching the sample, the sample must have come from one of those 7, 1 of whom is Stephen Lawrence, 6 of whom aren't.
Dr Jekyll said:
No, the statement was 'the chance of the sample not being from Stephen Lawrence was 1 in a billion'.
If there are 7 people in the world matching the sample, the sample must have come from one of those 7, 1 of whom is Stephen Lawrence, 6 of whom aren't.
Only if you can randomly pick 7 people out of the world and have them all be the ones with matching dna. Which you can't. A random 1 billion people would have one that matches. Thus: 1 in a billion chance.If there are 7 people in the world matching the sample, the sample must have come from one of those 7, 1 of whom is Stephen Lawrence, 6 of whom aren't.
otherman said:
Only if you can randomly pick 7 people out of the world and have them all be the ones with matching dna. Which you can't. A random 1 billion people would have one that matches. Thus: 1 in a billion chance.
That makes a one in a billion chance of a random person matching the sample, I can understand that. But the claim was 'one in a billion chance of the sample NOT being from Stephen Lawrence.If have a blood sample which is from one of seven people, the chance of it being any particular one of them is 1 in 7, the chance of it not being from any particular one is 6 in 7.
Dr Jekyll said:
otherman said:
Only if you can randomly pick 7 people out of the world and have them all be the ones with matching dna. Which you can't. A random 1 billion people would have one that matches. Thus: 1 in a billion chance.
That makes a one in a billion chance of a random person matching the sample, I can understand that. But the claim was 'one in a billion chance of the sample NOT being from Stephen Lawrence.If have a blood sample which is from one of seven people, the chance of it being any particular one of them is 1 in 7, the chance of it not being from any particular one is 6 in 7.
carmonk said:
But 6 in 7 was never mentioned other than on this forum. What the prosecutor said is that there is a one in a billion chance of it not being from SL. So are you saying that sounds very high? If so, I'd agree. Then again, it depends what was factored into that quote. Is that just by the DNA, or the DNA plus fact that SL happens to be the victim in the case? If the latter then the chance factor will increase by the ratio of people matching the DNA to those not matching and that could account for there being a 1 in a billion chance that the blood did not come from SL.
It wasn't the prosecutor who said it, it was the DNA expert. The fact that SL is the victim in the case is totally irrelevant unless you presuppose the accused were responsible.There are lots of arguments about these calculations.
If one assumes that the figure is correct if the total population of the world is considered then the statement suggests that the 'other' 6 ones with identical DNA are spread around the world more or less evenly, one on North America, one on the South, then there's Asia, Africa, Australasia and possibly Antarctica. But that's not how it works.
I've read that the most likely place for someone with identical DNA is on the same bus as you, the next street or, in this case, the next estate. It is not very likely of course, but the one in a billion is a bit misleading.
If one assumes that the figure is correct if the total population of the world is considered then the statement suggests that the 'other' 6 ones with identical DNA are spread around the world more or less evenly, one on North America, one on the South, then there's Asia, Africa, Australasia and possibly Antarctica. But that's not how it works.
I've read that the most likely place for someone with identical DNA is on the same bus as you, the next street or, in this case, the next estate. It is not very likely of course, but the one in a billion is a bit misleading.
Dr Jekyll said:
carmonk said:
But 6 in 7 was never mentioned other than on this forum. What the prosecutor said is that there is a one in a billion chance of it not being from SL. So are you saying that sounds very high? If so, I'd agree. Then again, it depends what was factored into that quote. Is that just by the DNA, or the DNA plus fact that SL happens to be the victim in the case? If the latter then the chance factor will increase by the ratio of people matching the DNA to those not matching and that could account for there being a 1 in a billion chance that the blood did not come from SL.
It wasn't the prosecutor who said it, it was the DNA expert. The fact that SL is the victim in the case is totally irrelevant unless you presuppose the accused were responsible.
ked up and I can't really see that happening.Gassing Station | News, Politics & Economics | Top of Page | What's New | My Stuff