[ExI] Terrorist? Who can tell?

[Lee Corbin]

BillK writes

>> faulty memory, but I could have sworn that *all* those
>> arrested and convicted in the recent bombings were
>> born in the Middle East, and have the same ethnic
>> profiles that allow me to often recognize the origins
>> of people I meet.
>> Hence my guess that at the 95% level of confidence,
>> six such individuals would be chosen as "the probable
>> convicts" and the other six average Londoners of the
>> same age and sex chosen as the "non-terrorist" group.
>> And only 5% of the time would the group of Londoners
>> picked at random---which surely includes a very wide
>> variety of people, nothing so nearly homogeneous
>> (I thought) as the bombers' group---be identified as
>> "the terrorists" by an ordinary set of citizens seeing each
>> group in a line-up.
> 
> No, Lee. You wouldn't be able to do that in London.

I still find it too incredible to believe.  By your parting remark,

> Give the police and MI5 some credit please! If it was that easy,
> terrorists would be arrested as soon as they stepped outdoors.

I wonder if you understood the actual experiment that I
proposed. It was *not* in any way a kind of actual test
that could be put into practice. Quite literally, it worked
as follows. We take for group A the last six convicted
terrorist bombers in London, and as a control group B
take six males of the same age randomly from the city.

> If you walk the streets of London, or watch London TV news reports, in
> many cases you will only rarely see a white face. And that white face
> is often the news reporter.
> 
> Actual statistics are difficult to obtain as ethnic origin is a very
> sensitive subject for the government.
> Ethnic groups tend to group together in their own boroughs and
> statistics apply to the whole of the region. So saying that, overall,
> about 40% of the 8 million Londoners are from a minority ethic group
> can be misleading. In some areas it will be nearly 100% white and in
> other areas nearly 100% non-white.

Well, now you have me really confused! You say that many
ethnic groups are represented and that it may be that they
constitute only 40% of the population. Now *this* includes
*all* ethnic groups, doesn't it? E.g., people from Latin America,
from east Asia, from the Middle East, and from Africa. To take
the *last* possibility, isn't there a rather high chance that someone
in group B will be black?  

In short, you are claiming that the relative homogeneity of my
group A (or at least I thought so), would be insufficient to allow
for a 19 in 20 test.  Now if we *raise* the number from my
"six" to "twenty" (provided that there have been that many
Middle Eastern terrorist bombers so convicted), then the
laws of mathematical probability insist that group A and group
B would become more and more reliably distinguishable.
You don't agree?

> I agree that the group of six bombers don't look like a group of six
> white people resembling Hugh Grant. But neither do any other members
> of the non-white half of the London population.

Never was I supposing that all Londoners are white; I've
seen at least that much on television, even from the movies
of the 1970s.

Lee