5 Problem In this problem we will plot the ROC curve for the example that we did class. We had defined the following two random variables ๆ = D = = { T 1 0 = if sample is infected if sample is not infected { 1 The ROC curve plots the True Positive Rate (which (which is also 1-0 where theta is the specificity). Recall that 0 test is positive test is negative is also the sensitivity n) against the False Positive Rate Sensitivity or also referred to as True Positive Rate P(T = 1|D = 1) D(T 100

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=
=
=
=
Specificity or also referred to as True Negative Rate
P(T=0|D = 0)
P(T=0nD = 0)
P(D = 0)
True Negatives
1 - Prevalance
We assume that X|(D
0)~ Norm (50, 10) and X|(D = 1) ~ Norm(70, 15). In R there are
functions to obtain both the probability density function (pdf) and the cumulative distribution function (cdf)
of a random variable that has a Normal distribution. These functions are dnorm and pnorm. Review the
help files to see the parameters of these functions. In this problem you are required to do the following
1. Plot the pdf and the cdf of X|(D = 1) ~ Norm(70, 15) for values 20 to 120.
2. Let x* denote the cutoff value such that if X > x* then the test is positive test otherwise it is consid-
ered be negative. Plot the ROC curve for values of z* ranging from 52 < x ≤ 65.
3. If False Positive Rate and False Negative Rates are equally bad, determine the value of r*.
=
Transcribed Image Text:0 = = = = Specificity or also referred to as True Negative Rate P(T=0|D = 0) P(T=0nD = 0) P(D = 0) True Negatives 1 - Prevalance We assume that X|(D 0)~ Norm (50, 10) and X|(D = 1) ~ Norm(70, 15). In R there are functions to obtain both the probability density function (pdf) and the cumulative distribution function (cdf) of a random variable that has a Normal distribution. These functions are dnorm and pnorm. Review the help files to see the parameters of these functions. In this problem you are required to do the following 1. Plot the pdf and the cdf of X|(D = 1) ~ Norm(70, 15) for values 20 to 120. 2. Let x* denote the cutoff value such that if X > x* then the test is positive test otherwise it is consid- ered be negative. Plot the ROC curve for values of z* ranging from 52 < x ≤ 65. 3. If False Positive Rate and False Negative Rates are equally bad, determine the value of r*. =
5
Problem
In this problem we will plot the ROC curve for the example that we did class. We had defined the following
two random variables
n
=
=
=
D
=
{
T
1
0
=
if sample is infected
if sample is not infected
The ROC curve plots the True Positive Rate (which is also the sensitivity n) against the False Positive Rate
(which is also 1 - 0 where theta is the specificity). Recall that
{
1
0
test is positive
test is negative
Sensitivity or also referred to as True Positive Rate
P(T=1|D = 1)
P(T=1nD = 1)
P(D = 1)
True Positives
Prevalance
Transcribed Image Text:5 Problem In this problem we will plot the ROC curve for the example that we did class. We had defined the following two random variables n = = = D = { T 1 0 = if sample is infected if sample is not infected The ROC curve plots the True Positive Rate (which is also the sensitivity n) against the False Positive Rate (which is also 1 - 0 where theta is the specificity). Recall that { 1 0 test is positive test is negative Sensitivity or also referred to as True Positive Rate P(T=1|D = 1) P(T=1nD = 1) P(D = 1) True Positives Prevalance
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          The ROC curve plots the True Positive Rate (which is also the sensitivity ŋ) against the False Positive Rate.

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