Lecture 17-18!! Flashcards
Epidemiology definition decreiptive part and analytic part
Descriptive epidemiology features
• ‘Person, place and time’
• Observational
• What • Who • Where • When
The public health model
Analytic epidemiology features
• Associations: exposures and outcomes
• Causation
• Observational or intervention studies
• Why
Examples of descriptive epidemiology
Cross-sectional and ecological studies
Example of analytic epidemiology
Cohort studies
Case-control studies
Randomised-controlled trials
What is a cross-sectional study?
Measures exposures and/or outcomes at one point in time
What do we mean by a ‘point in time?’ - CSS
A particular date
( 18 August 2023)
A specific event
(visit to doctor, retirement)
A specific period of time
(in the past 12 months)
S ome examples of cross-sectional studies
New Zealand Health Survey
Census of Populations and Dwellings
Youth 2000 National Youth Health and Wellbeing Survey Series
What do cross-sectional studies measure?
Prevalence: the proportion of a defined population who have a disease at a point in time
Prevalence =
number of people with disease at a given point in time
______________________________________________________________________
total number of people in the population at that point in time
P revalence is affected by
incidence AND duration
What will decrease prevelance
- death or recovery
Cross-sectional studies can be used to____
- Describe prevelance (What is the prevalence of osteoarthritis in NZ? )
- Compare prevalence (What is the prevalence of osteoarthritis in NZ for people of different ages? | Has the prevalence of smoking changed over time among high school students? )
- To generate hypotheses (Which factors are associated with low back pain among nurses?)
-To plan ( Population of Nelson-Tasman- Marlborough)
Cross - sectional studies: what they measure, what they are used for
- Measure exposures and/or outcomes at one point in time
- Measure prevalence (affected by incidence and duration)
- Used to:
describe prevalence
compare prevalence
generate hypotheses
plan (e.g. health service delivery)
Cross sectional needs to be around
EXACTLY AT THE POINT OF ASSESMEMT
- at the SEPCFIC point in time!!!!!!
Limitations of cross-sectional studies
Temporal sequencing - (Exposure and outcome were assessed at the same time - which came first the chicken or the egg)
Measures prevalence not incidence
Not good for studying rare outcomes or exposures
Not good for assessing variable and transient exposures or outcomes
Limitations of cross-sectional studies - Not good for assessing variable and transient exposures or outcomes - examples of transient / variable and why their hard to measure
Pros of cross sectional studies
• Can assess multiple exposures and outcomes • Depends on your research question
• Prevalence, and distribution of prevalence in the population
• Stable exposures and outcomes
• Hypothesis generating
• Can be less expensive than some other study designs • Relatively quick
What do ecological studies do?
Compare exposures and outcomes across GROUPS not individuals
Individual level studies vs group level studies
Yes
What are ecological studies used for?
• To compare between populations
• To assess population level factors
• To consider hypotheses
Examples of ecological studies
L imitations of ecological studies
- Ecological fallacy (…derives from ascribing to individuals the characteristics of the group - can’t describe characteristics of the group towards an individual in the group)
- cannot control for confounding
- cannot show causation
Advantages of ecological studies
• Depends on the research question
• Population level exposures
• Consideration of hypotheses
• Data is often routinely collected
• May be relatively easy to do
• May be relatively inexpensive
Cross-sectional studies - summary
Assess prevalence
Temporal sequence
Not good for rare, variable or transient exposures or outcomes
Ecological studies - summary
Group level not individual level
Every data point is a population (not individual people)
Ecological fallacy
Measures of association
Guts of analytic epidemiology
How do we compare groups?
Through analytic study designs
Cross-sectional & Ecological
Cohort
Case-control
Randomised controlled trial
Fu ndamental characteristics and logic of analytical study designs can be described using ..
PECOT
GATE
PECOT and GATE describe…
Fu ndamental characteristics and logic of analytical study designs
What is PECOT?
The GATE frame
Source vs sample population
In ___ epidemiology we want to _____________ exposure ______ or _______ the _______ of the ________
In analytic epidemiology we want to quantify the degree to which an exposure increases or decreases the occurrence of the outcome
How many times as likely is the exposed group to develop the outcome than the comparison group?
Ratio of the incidences
- relative risk
What is the relative risk
Ratio of the incidences
Incidence of the exposed
__________________________
Incidence of the comparison
What is the null value - relative risk
Exposed and comparison have the same incidence of outcome
- equal occurrence of outcome in both groups
- Exposure doesn’t change occurrence of outcome, so no association between exposure and outcome
When the ratios are different for incidence in relative risk - risk factor vs protective factor
- Greater incidence of outcome in exposed group
- Greater occurrence of outcome in exposed group
- If outcome is bad, exposure is potentially a risk factor for the outcome
- Greater incidence of outcome in comparison group
- Greater occurrence of outcome in comparison group
- If outcome is bad, exposure is potentially a protective factor for the outcome
The (Exposed Group) were (Value) as likely to develop (Outcome) compared to (Comparison Group)
(Same interpretation if using incidence proportion or incidence rate)
4 factors needed to interoperable relative risk
- exposed group
- value
- outcome
- comparison group
How to calculate risk difference or attributable risk
Incidence of exposed - incidence of control
(Differences in the incidences)
(How many extra/fewer cases of the outcome in the exposed group are attributable to the exposure)
Risk difference (RD/AR)
Interpreting the risk difference
There were (value) extra/ fewer (outcome) in (exposed group) compared to (comparison group)
(Report differently for incidence proportion and incidence rate)
Difference in interpreting the risk difference for proportion vs rate
Relative risk vs risk difference
Relative Risk
- Clues to aetiology (causes)
- Strength of association
Risk Difference
- Impact of exposure
- Impact of removing exposure
Relative risk vs risk difference
Relative Risk
- Clues to aetiology (causes)
- Strength of association
Risk Difference
- Impact of exposure
- Impact of removing exposure
PECOT/GATE
- what does it do?
Makes explicit the logic of comparing
Describes key components of a study
Can use GATE to calculate measures of occurrence and association
Measures of association - difference between what RR and RD measure
