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3F Epidemiology FINAL > Screening, Testing And Clinical Decision Making > Flashcards

Screening, Testing And Clinical Decision Making Flashcards

1
Q

Primary prevention

A

Prevention of disease in those who do not yet have it

-immunization, diet, exercise, sun protection, public policies, purifying water supply, health fairs, counseling

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2
Q

Secondary prevention

A

Identification of those who have the disease but not yet developed signs and symptoms

  • shorten its life span, or if no curs, increase quality of life
  • cholesterol, prostate, breast exams, SCREENING PROGRAMS
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3
Q

Tertiary prevention

A

Prevention of complications in those with the signs and symptoms

  • reduce disability
  • rehabilitations, PT, respiratory therapy
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4
Q

Screening programs are considered _____ prevention

A

Secondary

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5
Q

Characteristics of a good screening test

A

Easy to perform, quick, inexpensive, safe

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6
Q

The probability of cases of a condition accurately identified by the screening test

A

Yield

-E.g. to detect 1 case of glaucoma, 100 must be screened

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7
Q

Ability of a test to distinguish between those who have the disease and those who dont

A

Internal validity (accuracy)

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8
Q

Generalizability

A

External validity

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9
Q

Repeatability

A

Reliability

-OHTS study-86% of first time abnormal fields were normal on second tests

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10
Q

The abiltiy of a test to correctly identify people with a disease

A

Sensitivity

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11
Q

Sensitivity proportions

A 
# of people with the disease who testpositive/# of people with the disease who are tested 
-positive/all diseased who are tested

TP/TP+FN

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12
Q

Ability of a test to correctly identify people without a disease

A

Specificity

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13
Q

Specificity proportions

A

TN/TN+FP

Number of people without the disease who test negative/number of people without the disease who are tested

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14
Q

4 possible outcomes for specificity and sensitivity

A

True positive
False positive
True negative
False negative

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15
Q

Screening for glaucoma at a health fair

A
  • screen 100 persons with icare tonometer and FDT matrix VF
  • criteria for failure-IOP >21 and VF defect
  • all 100 will later have complete eye exams at the clinic determine whether or not they truly have glaucoma-“gold standard”
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16
Q

What is the sensitivity and specificity: test glaucoma-20 true glaucoma, 10 true normal; test normal-5 true glaucoma, 65 true normal.

A

Sensitivity
20/25=80%

Specificity
65/75=87%

False negative
5/(5+20)=1-0.8 (sensitivity)
20%

False positive
10/(10+65)=1-0.87 (specificity)
13%

17
Q

Tests with both high sensitivity and specificity

A

It is difficult to find a test with both-there is often a trade off between the two

18
Q

A test with poor sensitivity

A

Many false negatives

-many people with the disease will pass the test

19
Q

A test with poor specificity

A

Many false positives

-many people without the disease will fail the test

20
Q

Emphasize sensitivity to minimize

A

False negatives

  • when there is a big penalty for missing the diagnosis
  • dangerous but tredaqtable conditions-HIV, syphilis, TB, brain tumors
  • when you are more suspicious of the disease (e.g. higher prevalence)
21
Q

Emphasize specificity to minimize ______

A

False positive

  • when treatment involves risk and costs. Before subjecting patients to chemo, tissue diagnosis (highly specific test) is required.
  • when you are less suspicious of the disease. E.g. lower prevalence
22
Q

Choosing between sensitivity and specificity: confrontation visual fields

A
  • higher specificity (if you’re normal, tour more likely to pass this test than a Humphrey visual field)
  • low sensitivity (patients with subtle field defects will not be identified because targets are easily seen)
  • good for general population
23
Q

Choosing between sensitivity and specificity: automated threshold visual fields

A
  • lower specificity-many normals will give abnormal results t first, due to learning curve
  • much higher sensitivity
  • use when there is a higher suspicion for glaucoma
  • do not use indiscriminately because of the time and costs of repeating “abnormal” fields on normal eyes
24
Q

How do we decide whether a test result is normal or abnormal

A

Cutoff points are chosen on a continuum between normal and abnormal
-want the test to be sensitive enough to diagnose disease but specific enough not to subject patients to unnecessary treatment

25
Q

How would sensitivity and specificity change if I used a cutoff point other than 21 for IOP in a glaucoma screening?

A

Abnormal=18

  • increase sensitivity
  • decrease specificity

Abnormal=30

  • decrease sensitivity
  • increase specificity
26
Q

PSA levels in black men to detect prostate cancer: sensitivity and specificity

A

The higher the PSA level, the more specific it is, the less sensitive it is

27
Q

Receiver operating curve (ROC)

A
  • plots sensitivity vs specificity
  • shows trade off between sensitivity and specificity across a range of cutoff values
  • S and S range from 0-100%
  • values that give the max combinations of S and S are located closest to the upper left corner
28
Q

ROC curves for multiple tests

A
  • better tests have curves that crowd toward upper left corner
  • larger area below the curve=more accurate tests
29
Q

Testing for glaucoma using different tests: ROC

A

On the ROC, OCT had the line closest to the upper left corner and more area under the curve
-GDX was considered the worst one

30
Q

Limitation of sensitivity and specificity

A
  • they are properties of the test, BUT DO NOT TAKE INTO ACCOUNT THE PREVALENCE of the disease
  • you perform a test for a very rare condition, even with a specific test, abnormal results are apt to be false positives
  • you perform a test for a common condition, even with a sensitive test, normal results are apt to be false negatives
31
Q

Predictive value

A

Takes into account sensitivity, specificity and prevalence of the disease in the population tested
-give a positive or negative result, what is the probability of having or not having the disease

32
Q

Positive predictive value

A

The probability of the patient HAVING the disease given a positive (abnormal) test result
-like S/S, also a proportion

TP/TP+FP

33
Q

Negative predictive value

A

The probability of the patient NOT HAVING the disease given a negative (normal) result

TN/TN+FN

34
Q

What is the PPV and NPV: test glaucoma-20 true glaucoma, 10 true normal; test normal-5 true glaucoma, 65 true normal.

A

PPV=20/30=67%
- there is a 67% probability that those who test positive will actually have glaucoma
NPV=65/70=92%
-there is a 92% probability that those who test negative actually not have glaucoma

THE TEST HAS MORE VALUE IN IDENTIFYING NORMALS THAN IDENTIFYING GLAUCOMA PATIENTS WHEN THE PREVALENCE IS LOW

Prevalence=25/100=25%

35
Q

The PPV of a test increases as the prevalence _____

A

increases

36
Q

The NPV of a test increases as the prevalence ____

A

Decreases

37
Q

Clinical decision making with snesitivety/specificity/PPV/NPV

A
  • you cannot perform or emphasize every test on every patient
  • you must consider the probability of a disease in your clinical setting before ordering a test for it
  • consider the predictive value of a test before performing or emphasizing it
38
Q

The prevalence of narrow angles (and angle closure glaucoma) is greater in older, female, Chinese, hyperopic, cataract patients. You measure and estimate the angles by Van Hericl as grade 1 (abnormal) in a myope and hyperopia, in a Caucasian and Chinese patients. Narrow angles are confirmed on gonio. For which patients is the test better at predicting of tru narrow angles?

A

The patient with more risk factors. If you see a grade 1 angle in a myope and in a hyperope, that grade 1 angle is going to be more a true narrow angle in the hyperope. Better PPV in patient with more risk factors for narrow angles.

DIFFERENT TESTS ARE MORE VALUABLE IN DIFFERENT POPULATIONS

39
Q

The prevalence of retinal tears is greater in myopes. You find a suspected retinal tear during a peripheral retinal exam in a myope and emmetropia. You are more likely to be correct if the patient is a ____

A

Myope

  • the PPV of a peripheral retinal exam is greater in myopes
  • binocular indirect ophthalmoscope should be emphasized more in myopes
  • FACTORS THAT INFLUENCE TEST SELECTION INCLUDE RISL FACTORS, SUSPICION, PREVALENCE, AND SEVERITY OF DISEASE

3F Epidemiology FINAL (5 decks)

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