Epidemiology

Question 1

Define epidemiology:

Answer 1

A public health discipline basic science which studies the DISTRIBUTION and DETERMINANTS of disease in POPULATIONS to control disease and illness and promote health

Question 2

Define the core function of epidemiology: pubic health surveillance

Answer 2

Surveying populations to find patterns of disease occurrence

• Data interpretation is a key skill, other key skills are designing & using data collection instruments, data management, and scientific writing and presentation

Question 3

Define syndromes surveillance system:

Answer 3

Looks for predefined signs/symptoms of patients related to track able but rare diseases/conditions

Question 4

Define epidemic:

Answer 4

Occurrence of disease clearly in excess of normal expectancy

Spans greater than a localized outbreak

Question 5

Define Passive Surveillance System

Answer 5

Relies on healthcare system to follow regulations on required reportable diseases

Question 6

Define active surveillance system:

Answer 6

Health officials go into communities to search for new disease cases

Question 7

Define Outbreak:

Answer 7

An epidemic limited to a LOCALIZED increase in occurrence of disease (aka cluster)

Question 8

Define Endemic:

Answer 8

The constant presence of a disease within a given area or population in excess of normal levels in other areas

Question 9

Define Pandemic:

Answer 9

An epidemic spread world-wide (global health)

Question 10

Define absolute difference:

Answer 10

A subtraction

Question 11

Define relative difference:

Answer 11

A ratio

Question 12

Define incidence:

Answer 12

New cases of disease

[aka Risk, aka Attack Rate, aka Cumulative Incidence]

Question 13

Define prevalence

Answer 13

Existing cases of disease + new cases of disease

Question 14

What causes prevalence to decrease?

Answer 14

If someone is cured or dies (removed from the pool)

Question 15

What causes prevalence to go up?

Answer 15

When someone receives therapy to stay alive with the disease, such as insulin to treat diabetes

Question 16

How do you calculate incidence?

Answer 16

(# of new cases of illness)/(# of people at risk of illness or in population)

[always subtract out (from the starting population, if known), those who’re not ‘at risk’ (already have the disease/outcome or are immune)]

Question 17

What can incidence also be referred to as?

Answer 17

Risk, attack rate, or cumulative incidence

Question 18

What is the equation used to calculate prevalence?

Answer 18

of existing cases of disease/# of persons in population

Question 19

Define absolute difference:

Answer 19

A subtraction of 2 frequencies

Ex. 45 surgeries in males and 17 surgeries in females… 45-17 = 28, males had 28 more surgeries OR 17-45 = 28 (absolute value), females had 28 fewer surgeries

Question 20

Define Relative difference:

Answer 20

A division of frequencies or proportions

Question 21

Give an example of a relative difference frequency using 45 surgeries and 17 surgeries in females

Answer 21

45/17 = 2.6X the number of surgeries for males than females

OR

17/45 = 38%; Females had only 38% of the number of surgeries as males did

Question 22

Give an example of a relative difference proportion using 45 surgeries in males and 17 surgeries in females

Answer 22

45 males with surgeries/ total number of males = X% surgeries in males

OR

17 women with surgeries/total number of women = X% surgeries in women

Question 23

Define risk

Answer 23

Probability of outcome in an individual group

Question 24

Explain how to calculate risk using smokers and nonsmokers as your example:

Answer 24

(# smokers with disease)/(total # of smokers)

OR

(# of nonsmokers with disease)/(total # of nonsmokers)

Question 25

Define absolute risk reduction (ARR):

Answer 25

The risk difference of the outcome attributable to exposure difference between groups

Question 26

How do you calculate absolute risk reduction (ARR)?

Answer 26

Good outcome% - bad outcome% = X%

The ARR tells you that for example the drug tested works X% better than the placebo

Question 27

How is the relative risk reduction (RRR) calculated?

Answer 27

(AAR)/(R of the unexposed)

Ex. AAR/outcome of placebo = X%, so the drug lowers your risk of disease by X%

Question 28

Define the number needed to treat/number needed to harm

Answer 28

Number of patients needed to be treated to receive the stated benefit or harm: 1/ARR = # needed to treat

Ex. Say ARR = 3.8% so, 1/.038 = 27 patients would need to be treated with the drug to reduce 1 disease/death case
Answer MUST be a whole number!!

Question 29

Define Risk Ratio (RR or relative risk):

Answer 29

Ratios of the risks from 2 different groups

Risk of outcome in exposed)/(Risk of outcome in the non-exposed

Question 30

What do risk, odds, and hazard ratios all have in common?

Answer 30

• All compare 2 groups and describe the likelihood of an event/outcome in 1 group compared to another

Question 31

What does it mean if a risk, odds, or hazard ratio is equal to 1?

Answer 31

The event/outcome is equally likely for both groups being compared

Question 32

What does it mean if a risk, odds, or hazard ratio is >1?

Answer 32

The event/outcome is MORE likely to occur in the comparison group

Question 33

How is a risk, odds, or hazard ratio interpreted if it is >/= 2?

Answer 33

Use the phrase “X” times greater for interpretation

• The comparator group has X times greater odds of getting the disease

Question 34

What are the 3 things to look for when interpreting ratios?

Answer 34

1) Group comparison orientation (drug vs. placebo or placebo vs. drug)
2) Direction of words (increased or decreased)
3) Magnitude (80% (1.8 times) or 20% (.8 times))

Question 35

Define Odds

Answer 35

Frequency of an outcome occurring vs not occurring

• The frequency of exposure vs frequency of not being exposed

[in a 2x2 table, divide A/C or B/D]

Question 36

What is the simplest way (shortcut) to calculate an odds ratio?

Answer 36

Cross multiply

A X D)/(B X C

Question 37

Attributable risk is also known as ______

Answer 37

Absolute risk reduction (ARR)

[defines the risk difference of the outcome attributable to exposure difference between groups]

Question 38

Calculation of incidence rate

Answer 38

of new cases of illness/person-time of people at risk of illness

[person-time: 100 person-years is 100 people followed for 1 year each; 10 people followed for 10 years each; 25 people followed for 4 years each, etc.]

Question 39

How would you interpret a RR, OR, or HR of 1.8?

Answer 39

80% increased risk/odds/hazard

Question 40

How would you interpret a RR of 0.25?

Answer 40

75% decreased risk/odds/hazard

Question 41

T/F: When looking at the confidence interval for a ratio, if BOTH values are on the SAME side of 1.0 (equality) — it is ALWAYS statistically significant!

Answer 41

True