Introduction to Epidemiology

Question 1

What are the 6 basic epidemiological terms?

Answer 1

• Mortality rate
• Incidence
• Prevalence
• Patterns of outcome occurrence
• Outcomes
• Exposures

Question 2

Define mortality rate and what is required to calculate it?

Answer 2

Mortality rates are death rates

Meaningful Statistics Need;

• A denominator population
• A time frame

e.g;
Requires location (rough size of population) and frequency of death

Question 3

Define incidence, its 2 factors and calculations?

Answer 3

Incidence - Number of new cases

2 factors;
- person-time

Incidence rate = Number of new people with outcome over a time period x 100,000 /
Total number of people in the group at risk

— n years of follow-up (e.g. 10-year cancer incidence
rate is I per 10,000 of population)

Incidence rate = Number of new people with outcome over a time period x 100,000 /
Total person-time for people in the group at risk

These give incidence rate within 100,000 people

Question 4

Define prevalence, its correlation to incidence, give its 2 factors and calculations?

Answer 4

Prevalence - Proportion of population that has disease

If a new case stays on it becomes prevalence, the higher incidence gets the higher prevalence also gets

1). Point: at a specified time (e.g. 1% of population
had COPD in 2010)

Point prevalence rate = Number of people with outcome at a point in time x 100 /
Total number of people in the group

2). Period: over a specified period (e.g. lifetime
prevalence of dementia 40%)

Period prevalence rate = Number of people with outcome during a time period x 100 /
Average number of people in the group

Question 5

Define patterns of outcome occurrence

Answer 5

• Sporadic: Occasional cases occurring irregularly
• Endemic: Persistent background level of occurrence (low to moderate levels)
• Epidemic: Occurrence in excess of the expected level for a given time period. Starts as an outbreak and becomes an epidemic
• Pandemic: Epidemic occurring in or spreading over more than one continent

Question 6

What are the different outcomes?

Answer 6

Outcomes;

• Death
• Hospitalisation
• First diagnosis with a disease
• Recurrence (e.g. cancer)
• Quality of life
• Surrogates (e.g. blood pressure, lung function, etc.)

Question 7

Define the types of exposures?

Answer 7

Exposures;

• Non-modifiable
— age, sex, genotype

• Modifiable
— smoking, weight, diet, alcohol consumption

• Interventions (a special kind of exposure)
— drug therapy
— surgery
— lifestyle advice

Question 8

Without a denominator how significant are death rates?

Answer 8

Without a denominator population and time death rates are meaningless

Question 9

RETURN TO INCIDENCE V PREVELANCE

Answer 9

CAUSE I CBA SOZ X

Question 10

If you want to control disease what epidemiological term should you focus on?

Answer 10

If you want to control disease you should focus on incidence to prevent more new cases (act as a preventative measure) then target prevalence and help current people who have the disease get rid of it until it no longer exists

Question 11

What does an increased diagnosis lead to?

Answer 11

Increased incidence (incidence may be same rate we are just aware of it now)

Question 12

How can we increase recovery?

Answer 12

By improving medication, procedures, rehabilitation, etc

Question 13

How can we reduce death rate?

Answer 13

By improving long-term management

Question 14

What diagram shows how the 6 basic epidemiological terms correspond with one another ?

Answer 14

epidemiologists bathtub

Question 15

What is the effect estimate calculation for Risk?

Answer 15

Risk:
Number of outcomes in a group x 100 /
Number of people in the group

Question 16

What is the effect estimate calculation for Relative Risk?

Answer 16

Relative risk (RR; Risk ratio):
Risk in exposed /
Risk in unexposed

Question 17

What is the effect estimate calculation for Relative Risk Reduction?

Answer 17

Relative risk reduction (RRR):

(1 - Relative risk) x 100

Question 18

What is the effect estimate calculation for Absolute Risk Reduction?

Answer 18

Absolute risk reduction (ARR; Risk difference):

Risk in unexposed - Risk in exposed

Can equal this to zero and work out risk in unexposed or exposed if have Absolute risk reduction value

Question 19

What is the effect estimate calculation for Number needed to treat?

Answer 19

Number needed to treat (NNT); - Use in planning resources

1 / Absolute risk reduction

Question 20

What are confidence intervals?

Answer 20

“A confidence interval can be thought of as a range of
plausible values”

Questions how confident we are with a certain measurement

Question 21

What is significant about values nearer the limits in confidence intervals than those in the middle?

Answer 21

Values near the limits less plausible than those in the middle (in margin of error

Question 22

What does the wider the interval mean?

Answer 22

The wider the interval the greater the uncertainty

Question 23

What does the higher the line in confidence intervals mean?

Answer 23

The higher the line, the more plausible the value

Question 24

How are relative risk calculations used when making new medicines?

Answer 24

When you create a new medicine you get values for how confident you are that the treatment will work and percentage of those who may not

Question 25

What are the 4 benefits of confidence intervals?

Answer 25

Confidence intervals;

• Can be presented for any statistic/effect measure
• Represents range of plausible values
• More extreme values less likely
• Very useful in appraising published research

Question 26

Describe the hierarchy of evidence? (mention 2 trends)

Answer 26

Hierarchy of evidence is rating evidence

Factors at the top of the hierarchy/pyramid are more likely to influence clinical practice

Hence why we usually look at systematic review to influence clinical practice

As you increase up the Hierarchy of evidence the risk of being prone to confounding and bias decreases

Question 27

What 3 steps that are involved in cross-sectional studies ?

Answer 27

Cross-sectional study;
1). Sample a population

2). Estimate the proportion:
— Different exposures
— Different signs/symptoms
— Different outcomes

3). Use data
— to describe prevalence/burden
— to explore associations

Question 28

What 5 steps that are involved in cross-sectional studies ?

Answer 28

Case-control study;
1). Select cases with an outcome

2) . Select controls without the outcome
3) . Explore EXPOSURES in cases and controls (We have 1 group exposed and 1 group not exposed)
4) . Compare exposures in cases and controls
5) . Identify association

Question 29

What 4 steps that are involved in a cohort study ?

Answer 29

Cohort study;
• Select people without an outcome

• Classify according to an exposure

• Follow-up
— Prospective
— Retrospective

• Compare RISK of disease in exposed and
unexposed

Question 30

What 2 steps that are involved in a Randomised Controlled Trial (RCT) and when are they done?

Answer 30

Randomised controlled trial (RCT);
• Random allocation
— Intervention
— Control/comparator

• Compare RISK of outcome in intervention and
control groups

Usually done when testing new drugs

Question 31

What do we now ethically try to avoid using in Randomised Controlled Trials (RCT) ?

Answer 31

Try to stay away from using placebos and instead use old drug vs new one to compare

Question 32

What are the objectives of each study design?

Answer 32

Objectives;

RCT - Treatment effect

Cohort - Cause, Prognosis, Incidence

Case-control - Cause

Cross-sectional - Prevalence

Question 33

What is a confounding variable?

Answer 33

Confounding variable;
True relationship “confused” by a third factor

i.e - Ice cream confused relationship between Season/Weather and Murder

Question 34

What are Bias?

Answer 34

Bias;
• Systematic error 
— what data are collected 
— how data are collected 
— how data are analysed 
— how data are interpreted 
— how data are reported

Question 35

What does Bias lead to?

Answer 35

• Bias leads to wrong conclusions concerning:
— Effectiveness
— Causation