PHEPB Ecological and cross-sectional studies: measuring health and disease Flashcards
Observational studies questions usually fall into one of two camps:
- descriptive studies
- analytical studies
What are descriptive studies?
Descriptive studies: try to describe something about the disease process
- how does the risk of developing the disease vary over time? (→ trends)
- how does it vary from place to place?
- how does it vary with respect to certain characteristics of the individuals, such as age, sex or occupation group?
- include ecological and cross-sectional studies
Observational studies questions usually fall into one of two camps:
- descriptive studies
- analytical studies
What are analytical studies?
analytical studies= analysing instead of just describing
Do persons with the characteristic have the disease more frequently than those w/o the characteristic? (cross-sectional studies)
Do persons w the characteristic develop the disease sometime in the future more frequently than those w/o the characteristic (longitudinal/cohort studies)
Do persons with the disease have a characteristic more frequently than those without the disease? (case-control studies)
What is the key difference between an analytical and descriptive study?
The key difference between a descriptive study and an analytical study is the research question being asked.
Descriptive studies aim to describe the subject of the study, while analytical studies aim to determine the causes or relationships between variables
What is incidence?
Incidence = number of new cases of a specific health condition or disease that develop in a defined population during a specified time period.
It is a measure of the risk of developing the condition over a specific time period, and also is a measure of rate.
Incidence is typically calculated by dividing the number of new cases by total pop at risk during the same time period.
What is point prevelance?
Point (period) prevalence = the number of cases of a disorder present in a defined population at a given point in time.
Calculated by dividing the number of people w the condition by the total population.
Prevalence is often expressed as a percentage or a rate, such as the number of cases per 100,000 people.
Period prevalence is a useful measure of the burden of a particular disease in a population over a specific period and can help inform public health policies and resource allocation.
Use this diagram to explain how we measure health or disease occurence
- healthy population in lovely white cloud
- some of them develop the disease - they drop into the pool (incidence)
- they join the people who have the disease already (prevalence)
- the pool of prevalent cases - volume depends on duration and prognosis
Compare what these 2 graphs tell us
Left graph tells us that UK has the most people with TB and Estonia has the least. the graph fails to tell us in which country the risk of TB is higher. Graph only has NUMERATOR data (not denominator data - the total population which will allow us to work out proportion)
Right graph now shows denominator data, it tells us the prevalence which is commonly expressed as per 100,000 - a fixed denominator per country.
Describe natural history and sources of health data
If you want to see people who have a diagnosis then hospital records are the best source of data
Some who have the condition may not be seeking care so will not show up in GP or hospital records, this is when we have to recruit people to do observational studies: interviews, questionnaires, health surveys and cohort studies
What is Health Survey for England (HSE)?
Monitors trends in the nation’s health and care. The survey consists of an interview, followed by a nurse visit who takes some measurements to provide info
* Annual data collection at one point in time from individuals
* No follow-up of individuals
* random selection of households within postcodes
* individuals are invited to participate
* Representative of population in England
What kind of study is HSE?
Cross sectional;
- measures individual prevalence of exposure (aka risk factor) or outcome
- point prevalence or period prevalence
- descriptive if outcome not reported in relation to exposure, or if exposure not reported in relation to outcome
- analytical if disease prevalence compared by exposure / risk factor status- ie see below
How to calculate period prevalence?
Eg period prevalence of hypertension in a certain pop over a period of one year: use data to identify all diagnosed w hypertension at any time during the year, regardless of recovery.
Total number of individuals w hypertension at any point during the year / total population size= period prevalence
eg 100 hypertension individuals at any time during the year in a population of 1000–> (100/1000)=10%.
What is an ecological study?
An ecological study is an observational + analytical study. Focuses on links between exposures and outcomes by comparing groups/populations rather than individuals.
Data on exposures and outcomes are collected for a group, usually based on aggregate data sources such as vital stats or surveys. The exposure and outcome data are then compared across different groups or populations to identify links
Ascertainment of health outcome and risk factor status need not be from the same data source
What are the benefits and limitations of ecological studies?
Ecological studies can be useful for generating hypotheses on relationships between an exposure and an outcome at a population level.
Useful for examining the impact of social and environmental factors on health outcomes.
However, ecological studies are also have ecological fallacy= potential for incorrect inferences about individual-level relationships based on group-level associations. Cannot comment on individual exposure and risk of outcome
In order to determine if link= causation, we need to dig deeper, eg group the data into quintiles to help form more individual level relationships
What is mortality rate and how is it calculated?
How can we fairly compare mortality, eg for breast cancer in europe?
What is standardised rate?
Standardised rate has a direct and indirect method. What is the direct method?
ans= b and b
Standardised rate has a direct and indirect method. What is the indirect method?
