Probability: The sensitivity and specificity of the polygraph

[xclusive229]

I get probability for the most part so I think this question is only confusing me because I'm trying to evaluate it too deeply. Please get me started ...

The sensitivity and specificity of the polygraph has been a subject of study and debate for years. A 2001 study of the use of polygraph for screening purposes suggested that the probability of detecting a liar was .59 (sensitivity) and that the probability of detecting a "truth teller" was .90 (specificity). We estimate that about 20% of individuals selected for the screening polygraph will lie.
a. What is the probability that an individual is actually a liar given that the polygraph detected him/her as such? (Show me the table or the formulaic solution or both.)

b. What is the probability that an individual is actually a truth-teller given that the polygraph detected him/her as such? (Show me the table or the formulaic solution or both.)

c. What is the probability that a randomly selected individual is either a liar or was identified as a liar by the polygraph? Be sure to write the probability statement.

 

[Deleted member 4993]

I get probability for the most part so I think this question is only confusing me because I'm trying to evaluate it too deeply. Please get me started ...

The sensitivity and specificity of the polygraph has been a subject of study and debate for years. A 2001 study of the use of polygraph for screening purposes suggested that the probability of detecting a liar was .59 (sensitivity) and that the probability of detecting a "truth teller" was .90 (specificity). We estimate that about 20% of individuals selected for the screening polygraph will lie.
a. What is the probability that an individual is actually a liar given that the polygraph detected him/her as such? (Show me the table or the formulaic solution or both.)




b. What is the probability that an individual is actually a truth-teller given that the polygraph detected him/her as such? (Show me the table or the formulaic solution or both.)




c. What is the probability that a randomly selected individual is either a liar or was identified as a liar by the polygraph? Be sure to write the probability statement.

What are your thoughts?

Please share your work with us ...even if you know it is wrong

If you are stuck at the beginning tell us and we'll start with the definitions.

You need to read the rules of this forum. Please read the post titled "Read before Posting" at the following URL:

http://www.freemathhelp.com/forum/th...Before-Posting

 

[stapel]

The sensitivity and specificity of the polygraph has been a subject of study and debate for years. A 2001 study of the use of polygraph for screening purposes suggested that the probability of detecting a liar was .59 (sensitivity) and that the probability of detecting a "truth teller" was .90 (specificity). We estimate that about 20% of individuals selected for the screening polygraph will lie.

a. What is the probability that an individual is actually a liar given that the polygraph detected him/her as such? (Show me the table or the formulaic solution or both.)

The "showing" is your department (like was explained in the "Read Before Posting" thread that you read before posting). So:

You've done the box with the rows and columns of probabilities. What have you come up with?

Please be complete. Thank you!

 

[xclusive229]

I haven't gotten anything to start with. I thought I understood probability but when I started looking at this problem, I am not sure where to begin to set it up. Sorry if that a little confusing.

 

[stapel]

I haven't gotten anything to start with. I thought I understood probability but when I started looking at this problem, I am not sure where to begin to set it up. Sorry if that a little confusing.

So you're not in a probability or statistics course, and are needing links to lessons so that you can learn? What topics, if anything, have you studied in probability? How far back do we need to go? What series of lessons have you already tried studying?

Please be specific. Thank you!

 

[tracy72]

What are your thoughts?

Please share your work with us ...even if you know it is wrong

If you are stuck at the beginning tell us and we'll start with the definitions.

You need to read the rules of this forum. Please read the post titled "Read before Posting" at the following URL:

http://www.freemathhelp.com/forum/th...Before-Posting

I am working on this same problem. For "a" this is what I have:

.59x.20/(.59x.41+.10x.90)=0.3555288

am I any where close to the correct information/answer?