Chapter 5(from in class packet)

Question 1

why do we screen for disease?

Answer 1

to detect disease before there are signs or symptoms in order to REDUCE morbidity and mortality rates

Question 2

What is screening?

Answer 2

the application of a disease-detection test to people who are as yes asymptomatic

Question 3

What is the purpose of screening?

Answer 3

to classify individuals with respect to their likelihood of having a particular disease

Question 4

Can screening tests also be used as diagnostic tests?

Answer 4

YES

Question 5

Diagnosis involves what?

Answer 5

involves CONFIRMATION of PRESENCE or ABSENCE of disease in someone suspected or at risk of disease

Question 6

Screening is generally done among what type of individuals?

Answer 6

individuals who ARE NOT SUSPECTED of having disease

Question 7

What are some popular screening tests?

Answer 7

• mammography
• colonoscopy
• fecal occult
• pap smear
• PPD
• A1C

Question 8

What are the requirements for a Screening Test?

Answer 8

• should be relatively SENSITIVE and SPECIFIC
• should be simple and INEXPENSIVE
• should be VERY SAFE
• must be ACCEPTABLE to subjects and providers

Question 9

People who are being screened are?

Answer 9

• generally NOT patients
• NOT sick
• AREN’T expecting treatment

Question 10

What are the General Principles of Screening (by WHO)?

Answer 10

1. the condition should be an IMPORTANT health problem
2. there should be a TREATMENT for the condition
3. FACILITIES for diagnosis and treatment should be available
4. there should be a LATENT STAGE of the disease
5. there should be a TEST or EXAMINATION for the condition
6. the test should be ACCEPTABLE to the population
7. the natural HISTORY of disease should be ADEQUATELY UNDERSTOOD
8. there should be an AGREED POLICY on whom to treat
9. the total cost of finding a case should be ECONOMICALLY BALANCED in realtion to medical expenditure as a whole
10. Case-finding should a CONTINUOUS PROCESS not just a “once and for all” project

Question 11

How good is the test?

Answer 11

should be VALID and RELIABLE

Question 12

What is the term that asks, “How well does the test measure what it is supposed to measure?”

Answer 12

validity

Question 13

Reliability is what?

Answer 13

REPEATABILITY

Question 14

What is the term that asks, “How well does the test do in different populations?”

Answer 14

reliability

Question 15

What is seen in the “perfect world”?

Answer 15

TRUE POSITIVES AND TRUE NEGATIVES

Question 16

What is seen in the “real world”?

Answer 16

FALSE POSITIVES AND FALSE NEGATIVES

Question 17

People who are NOT diseased but have a POSITIVE test

Answer 17

FALSE POSITIVE

Question 18

People who really HAVE disease, but have a NEGATIVE test

Answer 18

FALSE NEGATIVE

Question 19

ability of the test to identify those who are diseased in the screened population

Answer 19

sensitivity

Question 20

the ability of the test to identify those who do not have the disease

Answer 20

specificity

Question 21

What is the overall accuracy of the test?

Answer 21

TP+TN/ TP+TN+FP+FN

Question 22

Sensitivity should be INCREASED when?

Answer 22

• the penalty associated with missing a case is high
• the disease can be spread
• subsequent diagnostic evaluation are associated with minimal cost and risk

Question 23

Specificity should be INCREASED when?

Answer 23

• the costs or risks associated with further diagnostic techniques are substantial
• minimize false positives

Question 24

True or False. Sensitivity and specificity are able to predict the performance of the screening test in the population.

Answer 24

FALSE because sensitivity and specificity are NOT able to predict

Question 25

the probability that a person actually has the disease given a positive test

Answer 25

positive predictive value (PPV)

Question 26

the probability that a person do not have the disease given a negative test

Answer 26

negative predictive value (NPV)

Question 27

What is a predictive value?

Answer 27

measures whether or not an individual actually has the disease, given the results of a screening test

Question 28

What are the 3 things predictive value is affected by?

Answer 28

- specificity - prevalence of preclinical disease - sensitivity

Question 29

during sequential screening, if you take all the people who screened positive on the first test and give them a second test (of higher sensitivity and specificity) what happens to the net?

Answer 29

- net sensitivity decreases | - net specificity increases

Question 30

true or false. the ppv is maximized when used in "high risk" populations since the prevalence of the pre-clinical disease is higher than in the general population

Answer 30

true

Question 31

screening the general population for a relatively infrequent disease can be what?

Answer 31

- wasteful of resources and may yield few previously undetected cases

Question 32

a test must be _____ before it can be valid

Answer 32

reliable

Question 33

an invalid test can demonstrate ________ ________

Answer 33

high reliability

Question 34

what are the three sources of variation?

Answer 34

1. instrument variation 2. inter- observer variation 3. intra-subject variation

Question 35

the need for calibration or standardization

Answer 35

instrument variation

Question 36

changes in repeated bp measurements over TIME

Answer 36

intra-subject variation

Question 37

inconsistency of interpretation by two or more diagnosticians

Answer 37

inter-observer variations

Question 38

what is the deviation of the results from the truth?

Answer 38

bias

Question 39

what is the interval between "diagnosis" of disease at screening and when it would have been detected from clinical symptoms?

Answer 39

lead time bias

Question 40

to detect disease before there are signs or symptoms in order to reduce morbidity and mortality from disease

Answer 40

lead time bias

Question 41

do you increase life expectancy for lead time bias?

Answer 41

no, you just cause the disease early

Question 42

the average length of time a person lives after the diagnosis with the disease or condition

Answer 42

survival time

Question 43

What kind of bias is this: "volunteers may be healthier than people who don't volunteer"?

Answer 43

self selection bias

Question 44

What kind of bias is this: "persons who screen positive who are really disease free can be erroneously diagnosed with a disease, resulting in a more favorable long term outcome. results in the appearance of effective screening"?

Answer 44

over diagnosis bias