Cross-sectional and ecological studies

Question 1

What is Descriptive Epidemiology?

Answer 1

Concerned with the distribution of health related states of event
Allows you to describe whats happening to a particular health outcome for a person (age, occupation, gender), place (geographical location) and time (day, month, year, season)
Undertaken by observational studies - observing whats already happening in population, found in the first part of the public health model

Question 2

What is Analytic epidemiology?

Answer 2

Concerned with the determinant of health events, cause and effects between exposures and outcomes
Observational studies or intervention studies
They seek to answer the question in the public health model of why?
Test hypothesis or ideas that might have been generated or considered in descriptive epidemiology

Question 3

What is a Cross sectional study?

Answer 3

Measures exposures and/or outcomes at one point in a time (particular date, specific event, specific period) if it includes both we are assessing the exposures and outcomes all at the same time
Participants involved are not selected into the study due to their outcome/exposure, instead they try recruit everyone in the population they’re interested in or try recruit a cross section of the population

Question 4

What do cross sectional studies measure?

Answer 4

Cross sectional studies measures the prevalence of a disease in the population at the point in time
Can be uses to describe prevalence, compare prevalence, generate a hypothesis and to plan health service delivery

Question 5

What is the GATE frame?

Answer 5

Pictorial way of describing main elements in epidemiological studies
Triangle: source, blue part (population that study sample drawn from) and sample, orange part (met criteria and in study)
Circle: exposed group over the dotted line (who have the risk factor interested in) and comparison group under the dotted line (who do not have the risk factor)
Square: outcome
Time arrow changes accordingly due to exposure and outcome being measured at the same time in cross sectional study

Question 6

What is a limitation of the GATE frame?

Answer 6

Limitation = exposure and outcome assessed at the same time hence we cannot tell if the exposure or outcome comes first
e.g. did people have knee pain before they were obese or were obese and then developed knee pain?

Question 7

Limitations of cross sectional studies

Answer 7

Cannot tell us about the onset of the disease
Not good for studying rare outcomes or exposures
Not good for assessing variable or transient (may only last for a short time) exposures or outcome hence study may differ depending on when the cross sectional study occurs

Question 8

Why use cross sectional studies?

Answer 8

We use cross sectional studies as they can asses multiple exposures and outcomes at the same time, they may be the most appropriate study design depending on research question, good for stable exposure and outcomes, can be less expensive, relatively quick

Question 9

What are ecological studies?

Answer 9

Compare exposure and outcome measured at a group level not an individual level
The measure is indicative of a group as a whole, can’t be related back to an individual, no individual characteristics
Used to compare different populations, assess population level factors (air pollution and respiratory disease in a population), consider hypothesis but cannot confirm hypothesis

Question 10

Limitations of ecological studies

Answer 10

Can’t relate characteristics of that group to individuals in the group
Cannot control confounding (when relationship is muddled by another factor)
Cannot show causation
Uses to measure population level exposures, data is often routinely collected hence relatively easy to do and may be relatively inexpensive