China virus probability problem

[bookbraker]

Still sticking with merlin because of the way the question was asked.

[BAUS]

Thank you Rito for $100 in BTC.

 

BAUS

[KingRevolver]

Teddy kicking himself.   He was about to surprise Hawaiian Punch with a $100 slots freeplay.

[BAUS]

Teddy, you should familiarize yourself with this problem better if you visit the STD clinic frequently.

 

BAUS

[Teddy kgb]

If he has 78/22 neg/poshe will be wrong 21x

 

If he has 82/18 also wrong 21x

 

He has to be 79/21 beg/pos

 

And that leaves you with a 1/21 chance

 

What pct is that?

If I’m positive then I’m then part of a group with 20’others leaving us all with a 1/21 chance of being the 1

[BAUS]

that equation doesn't make it right.

Huh??

 

BAUS

[bookbraker]

Where's monkey at?

 

We need him now Rev you fkin asshole!

[evade]

Monkey is not going to come up with a different answer. It's a standard bayes probability problem.

[Teddy kgb]

It’s fvcking basic math

[mikeman]

Huh??

 

BAUS

Tom Brady completes 80% of his passes, all nfl qb's(including tom plus the rest are midgits who cant grip the ball), complete only 1%. If Tom brady throws a pass, what's the chance it's completed?

[BAUS]

Jesus Christ these posts...I could have won this contest tomorrow.

 

BAUS

[ERBtheGREAT]

Tom Brady completes 80% of his passes, all nfl qb's(including tom plus the rest are midgits who cant grip the ball), complete only 1%. If Tom brady throws a pass, what's the chance it's completed?

3.88%

[mikeman]

3.88%

Like I said, that would mean of the 30000 people who tested positive today, only 1164 really have the virus.

[BarryRunSome]

The virus test is apparently only 80% accurate. So 1/5 tests give the wrong answer.

 

Assume 1% of people have the virus.

 

If you get a positive test, what is the actual chance you have the virus?

 

$100 Bitcoin to first correct answer

80%

[14 Words]

My only pushback on the way the question was asked was that it didn't provide what % of the population had been tested. For example, it could have included the following additional info in bold:

 

Assume 1% of people have the virus and X% of the population has been tested. (where X is defined)

 

Instead, it only included the first part:

 

Assume 1% of people have the virus.

 

 

[rito]

My only pushback on the way the question was asked was that it didn't provide what % of the population had been tested. For example, it could have included the following additional info in bold:

 

Assume 1% of people have the virus and X% of the population has been tested. (where X is defined)

 

Instead, it only included the first part:

This is completely irrelevant.

[mikeman]

My only pushback on the way the question was asked was that it didn't provide what % of the population had been tested. For example, it could have included the following additional info in bold:

 

Assume 1% of people have the virus and X% of the population has been tested. (where X is defined)

 

Instead, it only included the first part:

I dont think that matters, the question said the test is 80% accurate, then it said  the test is positive what are the chances you are really positive? You've already declared an outcome - the outcome has an 80% chance of being right.

 

The question was not grab a random person and speculate about what it means if you're positive.

[Chi_Archie]

clearly alot of people need to stop gambling with any hopes of winning long term

[BAUS]

This thread has shed some light on reasons why people lose at sports betting.

 

BAUS

[Deemer]

Get Some (___)

 

Get Mathematical (___)

 

Get None (___)

 

-MT

[14 Words]

This is completely irrelevant.

 

That's fair I suppose, but for me it would've helped knowing the % tested because I got stuck on the idea that the 80% testing accuracy rate could potentially change as more people got tested. (For example, in relation to the current Covid crisis where most have not been tested and we're left to spitball real %'s.)

 

Essentially, I got stuck on the assumption that the 80% rate might have been based on an incomplete data set.. (i.e. < 100% of population) and thus I started adding in other variables into my probability equation to try and account for that.

 

However, I can understand why you or anyone else might find the need to know that info irrelevant or that I simply over complicated things in retrospect.

[rito]

80% accurate means 4/5 people will get an accurate result. 1/5 won't. This includes false positives and false negatives.

[mikeman]

80% accurate means 4/5 people will get an accurate result. 1/5 won't. This includes false positives and false negatives.

Fine, but that doesn't mean if you're positive, there is only a 3.88% chance you really are.  . the fact that if you tested negative, you could still be positive is not applicable either.

[14 Words]

80% accurate means 4/5 people will get an accurate result. 1/5 won't. This includes false positives and false negatives.

 

I understand that now. But again, I thought that 80% figure wasn't necessarily fixed but could be variable as more people got tested. That then led me down the fruitless road of introducing new variables into my probability equation which I could not solve for. My fault in over complicating matters, thanks for the opportunity.

[Miley Cyrus]

The test is 80 percent accurate whether you have the virus or not? If so.........

.01*.8/.(01*.8 + .99*.8) = .01.