Lecture 17-18!! Flashcards by Becky Ross

Epidemiology definition decreiptive part and analytic part

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Descriptive epidemiology features

• ‘Person, place and time’
• Observational
• What • Who • Where • When

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The public health model

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Analytic epidemiology features

• Associations: exposures and outcomes
• Causation
• Observational or intervention studies
• Why

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Examples of descriptive epidemiology

Cross-sectional and ecological studies

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Example of analytic epidemiology

Cohort studies
Case-control studies
Randomised-controlled trials

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What is a cross-sectional study?

Measures exposures and/or outcomes at one point in time

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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)

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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

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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

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P revalence is affected by

incidence AND duration

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What will decrease prevelance

death or recovery

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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)

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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)

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Cross sectional needs to be around

EXACTLY AT THE POINT OF ASSESMEMT
- at the SEPCFIC point in time!!!!!!

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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

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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

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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

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What do ecological studies do?

Compare exposures and outcomes across GROUPS not individuals

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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