4. Descriptive epidemiology

Question 1

Target population =

Answer 1

People you want to apply your results to
(e.g. everyone living in australia)

Question 2

Source population/sampling frame =

Answer 2

People from whom the population is selected
(e.g. everyone on autralian election roll)

Question 3

Sample =

Answer 3

People approached tot ake part in the survey
(e.g. random sample of those listed)

Question 4

Study population =

Answer 4

People who actually took part in the survey

Question 5

What is the real strength of randomization?

Answer 5

• The real strength of randomisation is that, on average, it will also balance these other unknown or poorly measured factors across the groups.

Question 6

Why is it important to have large groups in an RCT?

Answer 6

If the groups are small it is unlikely that all of the factors that could affect the outcome will be evenly distributed across the groups.

Question 7

Of non-randomised designs, the most common are historical controls.What happens in such a design? What are these designs also called? Name an example.

Answer 7

> health outcomes after introduction of a new treatment/preventive measure are compared to the outcomes experienced by the same population before the change in practice
(also sometimes called a pre–post study)

e.g. patient survival rates might be compared before and after the introduction of a new surgical technique

Question 8

What is a major problem with historical controls?

Answer 8

Assumes that the only (or most important) thing that has changed is the new legislation or the type of surgery, and that may not be the case.

Question 9

Why must participants be free of the outcome of interest at the start of the follow-up of a prospective/longitudinal cohort study?

Answer 9

to avoid reverse causality

Question 10

What are advantages of the prospective cohort study design?

Answer 10

• Outcome bias is prevented. Measurement of exposure is not biased by knowledge of outcome status.
• Multiple outcomes/risk factors in single study
• Rare EXPOSURES (do not read: diseases) can be studied

Question 11

What are disadvantages of the prospective cohort study design?

Answer 11

• People may have changed their behaviours over the intervening years (misclassification)
• Not good rare diseases
• follow-up time long enough?
• Costs
• Ensuring people who started to stay till the end: who is lost to follow up?
• Confounding in exposure/non-exposed? (e..g who are those who regularly use and those who do not regularly use their phones?)

Question 12

What are limitations to the retrospective/historical cohort design?

Answer 12

• requires good records of past exposure
• generally limited to studying mortality or cancer outcomes, given the lack of universal records for other non-fatal endpoints

Question 13

Shape case-control?

Answer 13

disease/no disease > exposure

Question 14

Adv case-control study?

Answer 14

• Quicker
• Good for rare outcomes
• often less burden to participants
• cheaper

Question 15

What is a disadvantage of selecting hospital controls in case-control group?

Answer 15

Drawback: their risk factor distributions may not reflect that of the source population from which the cases emerged

Question 16

Disadv case-control study?

Answer 16

• Selection bias in case (survivor effect) and control groups (risk factors not like source population)
• Recall bias
• not good rare exposures
• Reverse causation
• Not able to calculate RR - you cannot calculate the incidence
• Confounding

Question 17

Cross-sectional study: characteristics and major issue?

Answer 17

• may be conducted to gather information about any aspects of health and lifestyle
• participants should be recruited without knowledge of their exposure/disease status
• Reverse causality (establishing temporality) = major issue

Question 18

What type of data can you use for an ecological study?

Answer 18

• Can only use generalized, already existing data

Question 19

Why do we need descriptive data?

Answer 19

● To evaluate the occurrence of health behaviours and health conditions (disease)
- Time trends
- Specific population subgroups
● To provide a basis for planning and evaluation of interventions
● Descriptive data can be used for further analytic studies

Question 20

Name three types of descriptive studies

Answer 20

• Case reports / series
• Prevalence studies / surveys
• Health registries / routinely collected data

Question 21

What is meant with case reports/series?

Answer 21

• Detailed report of symptoms, diagnosis, treatment, and follow-up of individual patient(s)
• Important for the early identification of health problems (e.g AIDS)
• Can generate hypotheses about potential causes
• Case report: on 1 patient
• Case series: on more patients

Question 22

What is meant with a prevalence study/survey?

Answer 22

• Presence of a condition at a particular point in time (point prevalence) or period (period prevalence) in a defined population
  ● Total number of people with certain disease
  ● Distribution of risk factor (e.g. smoking, blood pressure, obesity) or other characteristic (e.g. seat belt use)

Question 23

By what factors is prevalence influenced?

Answer 23

● Incidence
● Disease duration
● Other factors, e.g. likelihood of diagnosis

Question 24

Why are prevalence studies important?

Answer 24

• To assess the burden of disease in a population and to assess the need for health services
• To compare the prevalence of disease across populations
• To examine time trends in disease prevalence or severity

Question 25

What happens when changes in diagnostic criteria for diseases and changes in coding procedures for morbidity take place?

Answer 25

Can lead to 'artificial' changes in prevalence (and incidence) figures.

Question 26

Name four examples of health registries/routinely collected data

Answer 26

- Mortality records - Hospitalisation records - GP records - Cancer screening data - Birth records - Child care data - Infectious disease surveillance - etc.

Question 27

Shape of a cross-sectional study?

Answer 27

Defined population > Gather data on exposure + disease simultaneously > four groups (all needed): + exp + disease, + exp - disease, - exp - disease, - exp + disease

Question 28

Shape of a prospective cohort study?

Answer 28

Defined population > choice/circumstance > 2 groups: exposed vs non-exposed > 4 groups (2 each): disease and no disease. E.g. Choice: smoking. 2 group: smoking, non-smoking 4 groups: disease, no disease.

Question 29

Shape of case-control study?

Answer 29

Retrospective Defined population >looking back at cases and controls > each having 2 exposed and non-exposed groups

Question 30

RCT shape?

Answer 30

Defined population > random allocation > 2 groups: exposed vs non-exposed > 4x disease vs not diseased

Question 31

Which study designs are observational: analytical/descriptive, which are experimental?

Answer 31

Descriptive, Analytical: Cohort Case-control Cross-sectional Descriptive, observational: With no comparison group Experimental: RCT, non-RCT

Question 32

What is a cross-over design also called?

Answer 32

Two-period design or AB/BA design

Question 33

What are conditions for a cross-over study? What is the period called between treatment and control period?

Answer 33

- Can only be used if the exposure has no long lasting effect - Can only be used for outcomes that are reversible and that can change within a short time period ‘wash-out’ period

Question 34

What is a community trial? By whom is it executed? What is usually the purpose?

Answer 34

* Trial in the population, often focused on primary disease prevention * Unit of randomization are communities (e.g. towns, schools), not individuals -> Intervention is provided by e.g. GPs, community health centers, local outpatient facilities. * Suitable design for testing lifestyle interventions that cannot be allocated to individuals

Question 35

Quasi-experimental study = ? Why use it?

Answer 35

studies that aim to evaluate interventions but that do not use randomization. -> are less expensive and require fewer resources

Question 36

Disadv RCT?

Answer 36

* Relatively high costs * Rare disease outcome cannot be studied because of limited duration * Cannot be used for non-modifiable risk factors (e.g. genes, birth weight) * May be unethical, e.g. virus infection, smoking, sexual behavior * Wrong ‘time window’ of exposure * Not the full range of exposure can be studied

Question 37

What study design to use when studying non-modifiable risk factors?

Answer 37

Cohort study

Question 38

Purpose cohort study? Example?

Answer 38

- Evaluate the occurrence of disease in a carefully defined group of people (monitoring) - To investigate the causes of disease and to establish links between risk factors and health outcomes (etiology) EPIC (europe)

Question 39

What do you do in a historical cohort study?

Answer 39

* Identify a population and observe events as they occur * Retrospectively determine their exposure status from historical records

Question 40

Drawbacks Ecological study?

Answer 40

1. Populations differ in many ways other than the characteristic of interest 2. Results may not apply to the individual.

Question 41

Cross-sectional study: adv vs disadv?

Answer 41

Adv: - relatively simple - cheap - quick - minor ethical issues Disadv: - not rare disease - hard to establish temporality (which came first: exp-disease ?)

Question 42

Nested case-control study = ?

Answer 42

Cases of a disease that occur in a cohort are identified and, for each, a specified number of matched controls is selected from among those in the cohort who have not developed the disease by the time of disease occurrence in the case