Part 2: Types of Studies Flashcards
What are the 4 different studies?
- RCT
- Cohort
- Cross-sectional
- Ecological
What is a longitudinal study?
A study which goes through a period of time (over a long period of time)
What is the opposite of longitudinal study?
Cross sectional study (one point in time)
Which occurrence type can longitudinal studies be associated with?
Incidence
Which occurrence type can cross sectional be associated with?
Prevalence
Which studies out of the 4 are longitudinal?
RCT
Cohort
Could be Ecological
Which studies out of the 4 are cross sectional?
Cross-sectional
Could be Ecological
What is the usual study objective of RCT?
Investigate the effects of different interventions (exposures) on dis-ease incidence in different group of individuals
What is the usual study objective of Cohort studies?
Investigate associations (effects) between risk factors (exposures) and dis-ease incidence in different groups of individuals.
What is the usual study objective of Cross-sectional studies?
To measure dis-ease prevalence in defined groups of individuals.
Investigate associations between exposures and dis-ease prevalence in the groups.
What is the usual study objective of Ecological study?
Investigate associations between exposures and dis-ease prevalence or incidence in different groups of populations.
Which studies have individuals?
RCT
Cohort
Cross-sectional
Which study sees groups of populations rather than individuals?
Ecological
What is the most useful application of the RCT?
Effect of interventions like in:
- New therapies
- Drugss
What is the most useful application of the Cohort?
Studying the causes of dis-ease incidence or the effects of interventions
What is the most useful application of the Cross-sectional?
Measuring the prevalence/burden of dis-ease in different groups and populations
What is the most useful application of the Ecological?
Studying trends and causes of dis-ease incidence and prevalence
Which studies are experimental?
RCT
Could be Ecological
What is the opposite of experimental?
Observational
Which studies are observational?
Cohort
Cross-sectional
Could be Ecological
What does observational mean?
That the study undertakers are only viewing the participants, not forcing them to use anything (ethical)
What does experimental mean?
We do not know the outcome (like a new drug) so it could be bad or good but we are essentially experimenting on people in the RCT trials
How is RCT allocated?
Random
How is Cohort study allocated?
Measurement
How is Cross sectional allocated?
Measurement (usually by questionnaire or survey)
How is Ecological allocated?
Could be random or measurement
What does random allocation give rise to?
No confounding, allocation non random error
What does measurement error give rise to?
Confounding (allocation non random error)
Which studies have confounding?
Cohort
Cross-sectional
Ecological
What is the weakness of longitudinal studies?
Long time give rise to
- maintenance error
- also $$$$$$$$$$$
What gives rise to cross sectional (quick) studies?
Quick,
- no maintenance issue
- cheap as $
What is the main strength of RCT? (1)
Limited confounding
What is the main strength of Cohort studies? (2)
Usually cheaper than RCT (even though longitudinal)
E measured before O so NO recall bias
What is the main strength of Cross-sectional studies? (3)
Cheap
Quick, no follow up so NO MAINTENENCE
Best design for assessing prevalence/burden of dis-ease in population
What is the main strength of Ecological? (3)
Cheap
Quick
Efficient for rare outcomes
If a study is generally quick (no follow up) what does this have a positive for?
No maintenance non random error
What are the main weaknesses of RCT?
Ethical limitations
$$$$$$$$ so normally small participants so more random error and could be statistically insignificant
Maintenance error common
Which studies have follow ups?
RCT
Cohort
Could be ecological if it is a collection of RCT’s
What can follow up’s lead to (the weakness)
Maintenance non random error
What are the main weaknesses of Cohort?
Confounding (due to measurement allocation)
Maintenance error (long term studies because exposure is not controlled by the invesitgators)
What is the main weakness of Cross-sectional studies?
Uncertain time sequence so reverse causality
If period prevalence, can be subject to recall bias
Confounding (allocation is by measurement; survey)
What is the main weakness of Ecological studies?
Confounding very common
