Epidemiology

Question 1

Define epidemiology

Answer 1

The study of the distribution and determinants of health-related states and events in human populations (not individuals).

The application of this study to disease control.

Question 2

What are some characteristics of epidemiological study?

Answer 2

data driven

systematic and unbiased approach

relies on careful observation and valid comparison between groups

draws on methods from other scientific fields

• biology
• economics
• social
• behavioural

Question 3

Describe ‘distribution’.

Answer 3

the frequency and pattern of events

frequency:

• number of events (counts)
• number of events in comparison to the size of the population (rates)

pattern:

• time patterns e.g., annual, weekly, monthly, daily
• place patterns e.g., geographic location, urban/rural differences, work/school
• personal patterns e.g., age, gender, sexual orientation, disability

Question 4

Describe ‘determinants’.

Answer 4

the causes or other factors that influence the occurrence of disease/other health related events.

helps to investigate the hows and whys of disease.

helps to assess the difference between different population groups and occurrence of disease.

Question 5

What are the 5 different health related states/events?

Answer 5

communicable disease
non-communicable disease
birth outcomes 
mobidity 
mortality

Question 6

Describe the applications of epidemiology.

Answer 6

Diagnosing the health of a community.

Giving practical and appropriate public health advice/interventions to control and prevent disease in the community.

Question 7

What are the 3 aims of epidemiology?

Answer 7

• Describe the pattern, distribution and severity of disease within a community
• Understand why disease is more common in some groups than others
• provide information necessary to provide interventions to control, prevent and treat disease

Question 8

Define the term ‘infection’.

Answer 8

infection: the replication of organisms in a host tissue, which may cause disease.

Question 9

Define the term ‘infectious disease’.

Answer 9

Disease caused by a pathogenic organism, which can be transmitted from one infected living organism (person or animal, or contaminated object, to a susceptible host’

Question 10

Define ‘non-communicable disease’.

Answer 10

• chronic diseases e.g. diabetes
• tend to last a long duration of time
• usually the result of multiple genetic, physiological, social and behavioural factors.

Question 11

Define the term ‘sporadic disease’.

Answer 11

disease that occurs infrequently and sporadically.

Question 12

What is the difference between endemic, epidemic, and pandemic disease?

Answer 12

endemic - consistently present in a certain region/population. Low spread.

epidemic - sudden increase in cases spreading through a large population/region e.g., whole country.

pandemic - sudden increase in cases spreading through multiple regions/countries/continents.

Question 13

Define the term ‘mortality’.

Answer 13

The number of deaths in a certain group of people over a certain period of time.

Question 14

Define the term ‘morbidity’.

Answer 14

Having the disease, or symptoms of a disease.

Also refers to the amount of disease within a population.

Question 15

What are the different types of risk factors in epidemiology?

Answer 15

• Fixed marker
• Variable risk factor
• Variable marker
• Causal risk factor

Question 16

Describe the term ‘fixed marker’.

Answer 16

Risk factors that cannot change e.g., sex, age, ethnicity.

Question 17

Define the term ‘variable risk factor’.

Answer 17

A risk factor that can change spontaneously or as a result of an intervention.

Question 18

Define the term ‘variable marker’.

Answer 18

A risk factor, that even when manipulated, doesn’t change the outcome.

Question 19

Describe the term ‘rates’ and why they are usual as a measure of disease?

Answer 19

Rates are a measure of the number of cases in a given period of time (usually per year), compared to the size of the population being measured.

they are useful as they allow the comparison of the occurrence of disease in populations that differ in size. E.g., comparing the rates of COVID in the UK and Australia.

Question 20

What is the difference between incidence and prevalence?

Answer 20

Incidence - the number of new cases occurring in a given period of time.

Prevalence - the total number of cases existing within a given period of time.

Question 21

Describe the two methods of reporting prevalence.

Answer 21

Point prevalence - the proportion of a population that has a disease within a specific point in time.

Period prevalence - the proportion of the population that has had the disease over a specific time frame e.g., past 12 months.

Question 22

How is point prevalence rate measured?

Answer 22

no. existing cases at a given point in time / total population X 10,100,1000 etc..

Question 23

How is period prevalence rate measured?

Answer 23

no. of cases during a given time frame / average population during that time X 10,100,1000 etc..

Question 24

Describe the two methods of reporting incidence.

Answer 24

• incidence proportion

- incidence rate

Question 25

Describe incidence proportion. | How is it calculated?

Answer 25

the proportion of an initially disease-free population, that develops the disease, or dies within a given time frame. No. new cases in a population in a given period of time / no. of disease free people in the populated at the start of the time frame.

Question 26

Describe incidence rate. | How is it calculated?

Answer 26

Also known as person-time rate. No. of new cases across a given time period / time each person was observed, totalled for each person.

Question 27

Describe some factors that can increase disease prevalence

Answer 27

- longer duration of disease - immigration of diseased people e.g., global travel - emigration of healthy people - improved diagnostics - prolongation of life

Question 28

Describe some factors that can decrease disease prevalence

Answer 28

- shorter duration of disease - highly fatal disease - development of cure e.g., vaccination - immigration of diseased people - emigration of healthy people

Question 29

What are the two kinds of epidemiological study?

Answer 29

- Descriptive (allows a hypothesis to be tested) | - Analytic (allows for the generation of a hypothesis)

Question 30

Describe the 5 W's of epidemiology and which type of study they relate to.

Answer 30

What - death, symptoms, hospitalisation etc. Who - who affected e.g., age, gender, race, ethnicity. Where - where did it occur? When - when was the pop. affected? time, day, month, year, term, season? - descriptive Why/How - causation, risk factors etc. - analytic

Question 31

Describe the categories of epidemiological study.

Answer 31

Experimental - randomised - non-randomised controlled trial Observational - descriptive - analytic (cohort, case control, cross sectional)

Question 32

Describe the hierarchy of epidemiological study designs (from top, to bottom)

Answer 32

``` randomised clinical trials prospective cohort retrospective cohort case-control studies cross sectional study ecological study case series case report ```

Question 33

Describe cross sectional studies

Answer 33

A snap shot of the population at a given time Measures prevalence of health outcomes and investigates risk factors/exposure

Question 34

Describe case control studies

Answer 34

compares groups with a specific health outcome with groups that do not have the outcome e.g., group of women with breast cancer compared to group of women without breast cancer. looks at differences in history of exposures.

Question 35

Describe cohort studies

Answer 35

Subjects investigated over a longer period of time with repeated monitoring Can be both retrospective and prospective Examines the relationship between exposure and outcomes within the cohort

Question 36

Describe ecological studies

Answer 36

assesses overall rates of disease/health outcomes in a population allows for larger scale comparison e.g., obesity rates between UK & USA

Question 37

What is a strength and weakness of ecological study?

Answer 37

Strength - quick and easy as uses pre-existing data Weakness - ecological bias as doesn't represent individual variation amongst the population or inter-population e.g., variables in the uK may be different to those in the USA.

Question 38

What is a strength and weakness of cohort study?

Answer 38

strength - can infer a cause/effect relationship between exposure and health outcome weakness - impractical as time consuming and expensive - high drop out rate

Question 39

What is a strength and weakness of cross sectional study?

Answer 39

strength - quick and inexpensive and no follow up required limitation - difficult to infer cause/effect relationship between exposure and outcome - data may become invalid due to frequent changes in disease

Question 40

What is a strength and weakness of case-control study?

Answer 40

strength - ideal for rare outcomes or diseases that have no clear aetiology as multiple exposures can be investigated. weakness - prone to various types of bias as requires recall of information in both groups

Question 41

Describe the term 'measure of association'.

Answer 41

A measure of association quantifies the relationship between exposure and outcome amongst two groups (in experimental study).

Question 42

Describe Relative risk/risk ratio (RR)

Answer 42

RR compares the risk of a health outcome in one group with that of another group. Allows the quantification of risk level between two groups, e.g., an exposed group and a non-exposed group. There will be a differentiating factor between the two groups.

Question 43

How do you calculate RR? | What does the RR score indicate?

Answer 43

Risk of disease in group of primary interest (e.g., exposed group) / Risk of disease in comparison group RR of 1.0 indicates identical risk RR of less than 1.0 indicates decreased risk for the exposed group RR of greater than 1.0 indicates increased risk for the exposed group

Question 44

A group of people (10,000) have been recruited for a study. There were 3000 smokers and 7000 non-smokers 410 smokers developed heart disease 300 non smokers developed heart disease Calculate the RR and interpret the result

Answer 44

risk of disease in the exposed group = 410/3000 - 0.137 risk of disease in the non-exposed group = 300/7000 - 0.043 RR = 0.137/0.0043 - 3.19 3.19 = 2.19 increased RR (or 219% increase) in the exposed group compared to non exposed group.

Question 45

Describe odds ratio.

Answer 45

Tells us how much higher the odds of exposure are among case-patients than among controls. Higher odds ratio = risk factor for outcome

Question 46

How is odds ratio calculated?

Answer 46

odds that a case was exposed / odds that a control was exposed A X D / B X C = odds ratio odds ratio of 1.0 = identical risk odds ratio greater than 1.0 = exposure increases risk odds ratio less than 1.0 = exposure decreased risk (or even is a protective factor)

Question 47

Describe hazard ratio

Answer 47

estimates the effect of treatment used when presenting results after a clinical trial hazard ratio = hazard in exposed group / hazard in unexposed group.

Question 48

Describe confident interval.

Answer 48

Measure/indication of precision.