Question

For this discussion board, you will be presented with information about a new screening test.

Scenario: A new hypothetical instantaneous screening test for marijuana has been developed to identify people driving under the influence. 100 drivers are stopped by police and screened. 15 people were actually under the influence of marijuana, while the remainder were not. Of the 15 under the influence, only 10 tested positive. Of those who were not under the influence, 40 tested positive.

Instructions initial post: For your post, please complete the following questions. Be sure to set up your two-by-two table. In your post, you must correctly explicitly state the context of every numeric answer by including a sentence of interpretation (for example: "98% of patients who truly have breast cancer will have a positive mammography screen")

1. What is the prevalence of driving under the influence of marijuana?
2. Calculate sensitivity and interpret.
3. Calculate specificity and interpret
4. Calculate positive predictive value and interpret.
5. If more people drove under the influence of marijuana, how would the positive predictive value change?
6. Calculate negative predictive value
7. Calculate the accuracy of the screening tool.

In addition to posting your answers to the above questions, use those answers to write an opinion about:

1. whether or not this is a reasonable screening tool for police to use to enforce laws regarding driving under the influence and why.
2. how this screening tool could be improved.

Answer 1

Answer-

The prevalence is 15% . It is the total number of individuals who are under the influence of marijuana . It is a+c x100.

Interpretations-

Sensitivity -66.6% individuals were under the influence of marijuana and tested positive for it.

Specificity - 52.9% were not under the influence of marijuana and tested Negative for it.

Positive predictive value- there is 20% chance that the individual tested positive for the test was actually under influence of marijuana.

Negative predictive value - 90% chance that an individual tested negative for the test actually is not under influence of marijuana.

If more people drove under the influence of marijuana,the positive predictive value will increase. It increases with increase in prevalance.

This screening tool has only 55% accuracy .the specificity is 53% and sensitivity is 67% . A good screening tool will have a sensitivity and specificity of 99.9% . Which would mean all the individuals tested positive will actually have the disease and 99% times individuals tested negative wont have the disease or influence of drugs. This screening tool is not reliable to enforce laws . It can be improved by increasing the specificity and sensitivity.

If this helps please give it a positive rating thank you!