FOM 6.2.2

Question 1

What are the three levels of prevention?

Answer 1

Primary - prevent disease from occurring

Secondary - Identify disease process early to prevent sequelae or initiate treatment (Screening for STDs)

Tertiary - Minimize mortality and morbidity

Question 2

What are the goals of screening?

Answer 2

Reduce morbidity and mortality

Question 3

What is lead time bias?

Answer 3

When extra follow up time is added to the screened group

Question 4

What is length bias?

Answer 4

This refers to the time it takes for a disease to manifest in clinical symptoms. A slower progressing disease may be easier to detect.

Question 5

What is overdiagnosis?

Answer 5

A form of length bias that pertains to slow growing cancers that includes prostate cancer. Cancers that are overdiagnosed can be cured but do not need to be. This is estimated at the population level. As screening increases and disease diagnosis increases the mortality due to disease should go down. In over diagnosis, the mortality rates would stay the same despite the increases.

Question 6

What is the validity of a test?

Answer 6

Ability to distinguish between who has a disease and who does not.

Question 7

What is sensitivity of a test?

Answer 7

The sensitivity is the ability of a test to correctly identify those who have disease.

Question 8

What is a problem and benefit with high sensitivity tests?

Answer 8

It catch most who have the disease, but it also may call some people positive who dont have the disease. In a test with high sensitivity a negative result will rule out the disease because they lay outside the spectrum of dieases.

Question 9

What is specificity?

Answer 9

It measures that ability of a test to correctly identify individuals who do not have a disease. There may also be false negatives, people who are negative that have disease.

Question 10

A test with high specificity can rule in what?

Answer 10

If there is a positive result it will rule in disease

Question 11

When measuring the sensitivity what is the equation?

Answer 11

Question 12

What equation do you used when calculating specificity?

Answer 12

True Negatives / (False Positives + True Negatives)

Question 13

Answer this question

Answer 13

You would want a test with high sensitivity so you can correctly identify all individuals with the disease since it is fatal if not discovered early

Question 14

What is positive predictive value?

Answer 14

Probability that disease is present given that test is positive

True Positive / (True Positive + False Positive)

Question 15

What is the negative predictive value?

Answer 15

Probability that disease is not present given that test is negative

Question 16

Colon cancer screening study in Nottingham England.

Hemoccult testing

Sensitivity 70% and specificity 75%

Prevalence is 1.2%

What is PPV? What is NPV?

Answer 16

Question 17

Also answer for negative predictive value

Answer 17

D - 840/3040

Negative predictive value is 6600/6960

Question 18

What is a likelihood ratio used?

Answer 18

When describing a function of a parameter given an outcome. Ex if a test is conducted to times and it hascorrectly diagnosed disease 10 times what is the likelihood that the test is good.

Question 19

If LR=1 what can be said about the test?

Answer 19

The test has no discriminatory value.

Question 20

What are desirable vaules for LR+ and LR-?

Answer 20

LR+ would like to have a value greater than 10 and LR- would like to have value less that 0.1. The tests could then be said to have high diagnostic value.

Question 21

What is sequential testing vs simultaneous testing?

Answer 21

Sequential testing - two steps. If test 1 negative then stop if positive then continue with more tests.
Low net sensitivity but high specificity

Simultaneous Testing - For screen a large group quickly

Overall test negative if both are neg and if one if positive then the test is positive.

High sensitivity and low specificity

Question 22

You friend asks you “if this tests says I am pregant , what is the probability that I am really pregnant?” What would you calculate?

Answer 22

Positive predictive value

Question 23

If your friend asks you “if the test says I am pregnant what is the probability that I really am?” What do you calculate?

Answer 23

Negative predictive value

Question 24

Your friend asks you “if I am really pregnant what is the probability that the test will discover that?” What you calculate?

Answer 24

Sensitivity

Question 25

Answer the following questions

Answer 25

First one the correct statement is A

Second one the correct statement is C

Question 26

Answer the following

Answer 26

Sensitivity is 25/700

Specificity is 9275/9300

PPV = 25/50

NPV = 9275/9950