Statistics question

[TallBill]

Ok, tomorrow I got picked for a "random" drug test. In these tests 10% of the company is randomly selected to pee in a cup.

Well this is the 5th such test that I've been randomly selected for in the last 16 months. Thats obviously well above the average.

So what are the odds me being tested 5 out of 16 months at a 10% chance? I just wanna have some numbers when I go in tomorrow.

Btw, no tests ever come up hot because I dont use drugs, because using drugs while in the Army is plain old dumb.

 

[virtueixi]

5/16

 

[reverend boltron]

How often are the tests given?

 

[TallBill]

monthly

 

[Minjin]

Military often uses the last digit of your social security number. Or are you saying that you are the only person picked each time?

Mark

 

[TallBill]

Originally posted by: Minjin
Military often uses the last digit of your social security number. Or are you saying that you are the only person picked each time?

Mark

I'm saying that over the last 16 months, I've had a 10% chance of being picked each month (supposedly) but I've been picked 5 times total.

 

[upsciLLion]

Use the negative binomial distribution. 15 choose 4 times .10 to the 5th times .9 to the 11th power = .0042835, so 0.43% chance. Less than one percent.

 

[TallBill]

Originally posted by: upsciLLion
Use the negative binomial distribution. 15 choose 4 times .10 to the 5th times .9 to the 11th power = .0042835, so 0.43% chance. Less than one percent.

Thanks, its been 6 years since I've done that math.

 

[Mojoed]

What's happening to you is probably legit. If the system is a truly random 10% pick, 1 out of every 235 people will be tested at the frequency you've been tested at.

 

[TallBill]

Originally posted by: Mojoed
What's happening to you is probably legit. If the system is a truly random 10% pick, 1 out of every 235 people will be tested at the frequency you've been tested at.

Yeah, we have roughly 150 people, so its not to far from being the extreme limit I suppose.