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Epidemiology Exam 2 > Screening In Medicine > Flashcards

Screening In Medicine Flashcards

1
Q

2 questions that patients should ask their doctor when a medical screening test is recommended

A
  1. how accurate is the test?

2. how confident are you in the results ? (that its a true positive?)

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2
Q

4 possible outcomes to screening

A

true/false positive

true/false negative

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3
Q

TP

A

true positive

the test correctly reports a positive result

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4
Q

TN

A

true negative

the test correctly reports a negative result

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5
Q

FP

A

false positive

the test incorrectly reports a positive result when the patient does not have disease

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6
Q

FN

A

false negative

the test incorrectly reports a negative result when the patient does have disease

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7
Q

describing the accuracy of a screening test

A
  1. sensitivity

2. specificity

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8
Q

sensitivity

A

how well a test can detect presence of disease when it is present

positivity of test in the diseased

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9
Q

relate sensitivity and proportion

A

proportion of time that a test is positive in a patient that does have disease

= TP / (TP+FN) x %
or
= A/A+C x %

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10
Q

specificity

A

how well a test can detect absence of disease when it is absent

negativity of test in healthy

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11
Q

relate specificity and proportion

A

proportion of time that a test is negative when patient does not have disease

a highly specific test has a low FP rate

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12
Q

calculate specificity

A

= TN / (TN+FP) x %
or
= D / (B+D) x %

TN/all non-diseased

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13
Q

what calculations answer how accurate a test is?

A

sensitivity

specificity

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14
Q

sensitivity and specificity are all about predicting ……?

A

accuracy of the test

not about predicting the patient’s disease state

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15
Q

factors to determine your confidence in the results of a test

A
  1. positive predictive values
  2. neg. predictive value

to describe the accuracy of prediction of disease

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16
Q

PPV

A

how accurately a pos. test predicts the presence of disease

PPV = TP/(TP+FP)
= TP/all pos. tests

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17
Q

NPV

A

how accurately a neg. test predicts the absence of disease

NPV = TN/(TN+FN)
or
= TN/all neg. tests

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18
Q

if community prevalence of a disease increases

A

of false neg./pos. can increase

PPV greatly increases

NPV slowly decreases

but sensitivity/specificity never changes because it’s about the test not the pop.

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19
Q

as you approach a prevalence of 100%

A

PPV will jump towards a 100% because any test can predict the disease since almost everyone has the disease

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20
Q

true negative/false negative

A

sensitivity

TP/(TP+FN)

21
Q

true negative/false positive

A

specificity

TN/(TN+FP)

22
Q

as sensitivity decreases, the _____ will decrease, why?

A

NPV

because FN is in both equations

23
Q

as sensitivity decreases, the _____ will decrease, why?

A

NPV

because FN is in both equations

24
Q

in what situation would the sensitivity/specificity and the PPV/NPV be the same for two different cities?

A

sensitivity/specificity is always the same because it’s about the test

PPV/NPV can only be the same if the prevalence of the cities is the same

25
Q

DA

A

diagnostic accuracy

also called DP

26
Q

DP

A

diagnostic precision

also called DA

27
Q

define DA

A

proportion of total screenings that a patient is correctly identified as a TP or TN

28
Q

DA equation

A

=(TP+TN) / (TP+FP+FN+TN)
or
= (TP+TN) / all patients

29
Q

LR

A

likelihood ratio

30
Q

define LR

A

ratio of the probability of a test result for a diseased person / divided by the probability of the same test result for a non-diseased person

31
Q

calculate LR

A

equation depends on what you’re calculating for

positive or negative results

32
Q

LR is a ratio of ______ .

A

2 probabilities

where the diseased persons always live in numerator

non-diseased always live in denominator

33
Q

LR+

A

positive test in diseased / positive test in non-diseased
or
sensitivity/(1-specificity)

[(A/(A+C)) / (B/(B+D))]

34
Q

LR+ is not

A

simple division

it is the division/ratio of 2 percentages

35
Q

LR-

A

negative test in diseased / negative test in non-diseased

(1-sensitivity) / specificity

36
Q

compare equations of LR+ vs. LR-

A

LR+ numerators A and B
sensitivity / (1-specificity)

LR- numerators C and D
(1-sensitivity) / specificity

37
Q

what should our LR+/LR- results be in a good test?

A

+ should be large

  • should be small
38
Q

LR+/- results to demonstrate the test is beneficial

A

LR+ >10

LR-<0.1

39
Q

a _____ test is always reliable, but a ______ test is not always valid.

A

valid

reliable

40
Q

interpret a LR+ of 1.0

A

the likelihood ratio, positive of 1.0. tells us that the test is just as likely to positive in diseased as it is to be positive in non-diseased

a equal likelihood of a positive test in diseased and positive test in non-diseased

LR- describes negative in diseased and negative in non-diseased

41
Q

define validity

A

ability to accurately discern between those who are diseased vs. non-diseased

42
Q

validity is analogous to ?

A

precision

43
Q

define internal validity

A

extent to which results accurately reflect the study population

44
Q

define external validity

A

extent to which results are applicable to other populations

45
Q

another term for external validity

A

generalizability

46
Q

define reliability

A

ability of a test to give the same result on repeated uses

47
Q

reliability is analogous to ?

A

reproducibility or consistency

48
Q

what is the impact of modifying the cut-off value on the sensitivity and specificity of a test?

A

increasing cutoff increases false negatives (increases specificity)

decreasing cutoff increases false positives (increases sensitivity)

when specificity is on the left

Epidemiology Exam 2 (6 decks)

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