Week 9

Question 1

mass screening

Answer 1

whole population or subset

Question 2

multiple or multiphasic screening

Answer 2

many screening tests at the same time

Question 3

targeted screening

Answer 3

groups with a particular exposure

Question 4

case-finding/ opportunistic screening

Answer 4

tested while at the doctors for another purpose

Question 5

3 ways to distinguish between normal and abnormal

Answer 5

1. normal as common
2. abnormal associated with disease
3. abnormal as treatable

Question 6

1. normal as common

Answer 6

Values that occur frequently are normal
Values that occur infrequently are abnormal
Normal distribution: 2.5% abnormal using + 2SD cut off
Percentile (95%): 95% normal and 5% abnormal

Question 7

2. abnormal associated with disease

Answer 7

Use of the distribution of measurements for both healthy/diseased people with an attempt to define the cut-off that separates the two groups
Results in some healthy people on the ‘abnormal’ side and some diseased people on the ‘normal’ side

Question 8

3. Abnormal as treatable

Answer 8

Definition of abnormal changes over time based on changing treatment thresholds

Question 9

before screening, disease must be

Answer 9

Relatively common (prevalent) disease
Several consequences
Early treatment produces better outcomes
Considered a problem by people
Natural history well-understood
Relatively long preclinical phase when disease could be detected by screening

Question 10

the screening test should be

Answer 10

Good accuracy OR high sensitivity and/or specificity 
Safe 
simple/logistically manageable 
Relatively cheap 
Acceptable to ‘healthy’ people

Question 11

positive results threshold- screening test

Answer 11

tend towards high sensitivity not to miss potential disease

Question 12

positive results threshold- diagnostic test

Answer 12

tend towards high specificity (true negatives)

more weight given to accuracy and precision than to patient acceptability

Question 13

positive result- screening test

Answer 13

indicates suspicion of disease (often used in combination with other risk factors) that warrants confirmation (diagnosis)

Question 14

positive result- diagnostic test

Answer 14

result provides a definite diagnosis

Question 15

in tests, we are most concerned about

Answer 15

false negatives

Question 16

true positive

Answer 16

disease present

test positive

Question 17

false positive

Answer 17

disease absent

test positive

Question 18

false negative

Answer 18

disease present

test negative

Question 19

true negative

Answer 19

disease absent

test negative

Question 20

sensitivity

Answer 20

probability of a positive test in people with the disease

Question 21

sensitivity F

Answer 21

true positive/total diseased

a/a+c

Question 22

specificity

Answer 22

probability of a negative test in people without the disease

Question 23

specificity F

Answer 23

true negative/ total non disease

d/b+d

Question 24

positive predictive value (PPV)

Answer 24

probability a person has the disease when the test is positive

Question 25

PPV F

Answer 25

true positive/total positive | a/a+b

Question 26

negative predictive value NPV

Answer 26

probability a person does not have the disease when the rest is negative we want high (near 100%) NPV to avoid false negative

Question 27

NPV F

Answer 27

true negative/total negative | d/c+d

Question 28

sensitivity and specificity

Answer 28

relate to the features of the test | Do not change with the prevalence of the disease

Question 29

PPV and NPV

Answer 29

do change with the prevalence of the disease | PPV will be low when prevalence is low

Question 30

O'briens labral tear test accuracy

Answer 30

Diagnosed via physiotherapists using the Active Compression Obrien test

Question 31

DST test accuracy

Answer 31

Used to diagnose depression

Question 32

Screening- length time bias

Answer 32

Screening often diagnoses diseases that are less aggressive than those present clinically Thus treatment needs to be safe and effective- as sometimes disease detected through screening wouldn’t present/be diagnosed clinically

Question 33

Screening- lead time bias

Answer 33

Early detection: disease diagnosis by screening before clinical presentation As a result there is lead time, extra time that you know you have the disease Thus ‘survival time’ should not be used to evaluate a screening test- as survival in screened individuals will appear longer. This is irrespective of whether screening affects the survival course or not

Question 34

chi squares

Answer 34

two categorical variables

Question 35

expected cell frequency

Answer 35

(row total x column total) / grand total

Question 36

df

Answer 36

(row - 1) x (column - 1)

Question 37

chi square test not valid if

Answer 37

more than 20% of the cells have expected frequency smaller than 5

Question 38

if more than 20% of the cells have expected frequency less than 5

Answer 38

use Yates continuity corrected chi squares