Epidemiology

Question 1

Definition of incidence

Answer 1

Number of NEW cases within population @ risk

Question 2

Prevalence is :

Answer 2

No. of old + new cases within population at risk

Question 3

Absolute risk (AR):

Answer 3

Number of events (good or bad)*
___________________________
Population within that group

*in treatment or control groups

Question 4

Relative risk :

Answer 4

Exposed
________
Non-exposed

Or
AR treatment group/ AR control group

Question 5

Absolute risk reduction (ARR)

Answer 5

AR control (placebo) group - AR test (treatment)

Question 6

Relative risk reduction (RRR)

Answer 6

ARC -ART
\_\_\_\_\_\_\_\_\_
ARC 
Or
1-RR

ARC= AR of control group ART= of treatment group 
RR= ART/ARC

Question 7

Sensitivity

Answer 7

True positive
________________________
True positive + false negative

= A/A+C

Question 8

Specificity

Answer 8

True negative
_______________
True negative + false positive

=D/D+B

Question 9

Number needed treatment

Answer 9

Average no.of patients that need to be treated to prevent 1 additional bad outcome
NNT=1/ARR (inverse of absolute risk reduction)

E.g number of pets that need to be treated for one of them to benefit compared with control

Lower the NNT the better the drug

Question 10

1 standard deviation =

Answer 10

68.2

Question 11

2SD=

Answer 11

95.4

Question 12

3SD=

Answer 12

99.7

Question 13

What are examples of measures of central tendency

Answer 13

Mean
Median
Mode

Question 14

What are examples of measures of dispersion

Answer 14

Standard deviation

Standard error of mean

Question 15

Positive predictive value (PPV) =

Answer 15

True positive
___________
TP + FP

Question 16

Negative predictive value =

Answer 16

True negative
_____
FN +TN

Question 17

Accuracy =

Answer 17

(True +)+(true -)
______________
TP+FP+TN+FN

Question 18

Name an interventional study.

Answer 18

Randomised controlled trial

Question 19

Types of observational studies

Answer 19

Prospective cohort study
Snapshot - cross sectional study
Retrospective

Question 20

Retrospective case study types

Answer 20

Case control - starts with disease

Retrospective cohort - starts with exposure

Question 21

Study that involves only the present

Answer 21

Cross sectional (snapshot)

Question 22

Study that involves :present —> future

Answer 22

Prospective cohort

Question 23

Study that involves past

Answer 23

Case control study
- 2 groups = one with disease/outcome & 1 w/o
Look back to assess statiscally significant difference in rate of exposure

Question 24

Main outcome measure in case control studies

Answer 24

Odds ratio

Question 25

Advantages of case control studies (5)

Answer 25

``` Cheap Quick & easy to conduct Good for disease with long latency periods Can asses multiple exposure Good for rare disease ```

Question 26

Disadvantages of case control studies (4)

Answer 26

More prone to bias - main expose is recall bias Can only asses 1 outcome or disease Cannot establish risk Cannot establish prevalence

Question 27

Case control vs cohort

Answer 27

cOhOrt - relatives are the same (relative risk is the same) - usually prospective, look forward in time, however can be retrospective cAse cOntrol - vowels at odds with another = Odds ratio Start with disease and look back in time Cohort - start with exposure Case control - start with disease

Question 28

What are cohort studies good for

Answer 28

Assessing prognosis RFs and harm

Question 29

Outcome measure in cohort studies

Answer 29

Relative risk ratio or relative risk

Question 30

Advantages of cohort studies (4)

Answer 30

Usually prospective Can establish risk directly Can assess multiple outcomes and diseases Good for rare exposures

Question 31

Disadvantages of cohort studies (4)

Answer 31

More expensive Longer/harder to conduct Not good for rare diseases Not good for diseases with long latency periods

Question 32

Case control vs retrospective cohort

Answer 32

Both retrospective CC- starts from outcomes and tries to study what the exposure was (Starts with disease) RC - starts with exposure Exposure already determined - tries to study association to disease

Question 33

High sensitivity =

Answer 33

Few false negatives

Question 34

Low sensitivity =

Answer 34

Many false negs

Question 35

High specificity =

Answer 35

Few false positive s

Question 36

Low specificity =

Answer 36

Many false positives

Question 37

Reasons for dropout from study

Answer 37

Dropouts more in placebo - - breakdown of double blind study. Or group in blinded trial accidentally revealed to researchers If similar dropout numbers in both - possible chance event

Question 38

Relative risk reduction =

Answer 38

1 - RR Or ARC-ART/ARC

Question 39

Types of randomised control studies

Answer 39

Single blinded - either researchers or candidates don’t know who’s using real tx Only one of them is blind top the information Double blinded Noth candidates and researchers are blind to the information

Question 40

Number needed to treat=

Answer 40

1/ ARR | ARR= ARC -ART

Question 41

Secondary attack rate

Answer 41

No. Of 2ry cases _______________ (All people in group - 1ry cases)

Question 42

Primary attack rate

Answer 42

No of 1ry cases/ total population at risk x 100

Question 43

Accuracy of a screening test

Answer 43

True positives + true negatives ____________________________ TP+TN+FP+FN

Question 44

Number needed to harm is

Answer 44

No of people who have to take a treatment for 1 of them to have an adverse effect