More Probabilities ...

[sunny-dave]

... but very practical ones this time.


You are invited to go for a screening test for an illness - you have no symptoms.

About 1% of the screened group will have the illness.

The test is 99% accurate at diagnosing people who have the illness.

You get a 'positive' result.

How likely is it that you actually have the illness?


99%?

That's what many people think.

[sunny-dave]

The true answer is "You just don't know" - until they share something that they will be very coy about ... which is the percentage rate of "false positives".

Say they eventually admit that this is about 2% of people scanned (not a bad rate actually).


This then means that (if you get a positive result) your actual chance of having the illness is ... about 33%. Not the 99% that they waved at you in the first place.


[ explanation :

scan 1,000,000 people

10,000 will have the illness and 9,900 will be given a (true) positive diagnosis

990,000 will not have the illness - 19,800 will be given a (false) positive diagnosis

you have an 1 in 3 chance of being in the 'true' group ]

[Psybbo]

Dave I now have 100% brain fade

[tonyav]

I need two ibuprofen now.

[Tilly2]

Am I ill, or not?

[Hopkirk]

I'm positive that I have the illness

[Tilly2]

I'm Rhesus negative.

[tonyav]

Is that a type of monkey, Yilly.

[Tilly2]

Yes, Yont. I'm a little monkey!

[anneasquith]

I'm Scottish !!!!

[tonyav]

Tilly2
Yes, Yont. I'm a little monkey!


I know !.

[Psybbo]

So am I Tilly, in fact, negative, negative, negative

[tonyav]

anneasquith
I'm Scottish !!!!


99% ?

[Tilly2]

:-)

[anneasquith]

no tony... 100% Scottish ,

[Tilly2]

[gness]

Will buying only black socks and having only one child make me more or less likely to have the illness?....x

[anneasquith]

how old is the child ?

[gness]

Tallulah...x

[Tilly2]

Probably Tallulah?

[Tilly2]

However.....?