Study Types Flashcards
What are the levels in the pyramid of evidence from strong to weak?
Sys Reviews-Meta-analysis (not narrative review)
RCTs
Cohorts studies
Case-control
Cross-sectional studies
Case series, case reports
Ideas, opinions, editorials, anecdotal
What are the two types of study designs & their subtypes?
Experimental- Randomised controlled trial
Observational- Cohort, case-control, cross-sectional
What does equipoise mean and why is it important?
Means you are not sure which treatment is more effective
Important b/c if you are certain one tx is better than the other, there are moral implications
What are the essential components of a RCT?
Control group (from same population)
Randomization
Fully blinded
Identical TX & outcome measurements
What are the steps to conducting a RCT?
- Conduct a literature search
- Statement of justification (justify why conducting study)
- Objective & hypothesis (specific & measurable)
- Identify outcome variables (what you are measuring)
- Define the experimental unit (ind. animal, groups, parts of animal)
- Define study population
- Define the inclusion & exclusion criteria (want cases & controls similar in all respects possible)
- Consult statistician (sample size calculations)
- Recruit & enroll subjects
10 Random allocation
11 Identify other sources of bias
12 data collection
13 data grooming & analysis
14 Publish the study
When a disease you want to study in a RCT is common, what type of enrollment can be used?
simultaneous enrollment
When a disease you want to study in a RCT is uncommon, what type of enrollment can be used?
sequential enrollment
What is the main reason for random allocation?
REDUCE BIAS
What are the ways sources of bias can be reduced?
Blinding of all study participants
Standardization
Random allocation of treatment groups
What is the purpose of performing a baseline comparison of the treatment groups?
confirm comparison groups are statistically the same
In which type of study (experimental vs. observational) are the treatment groups not assigned?
Observational
In which observational study are the study subjects healthy at the start?
cohort study
Cohort study
starting with healthy animals, we prospectively compare them to animals with different exposure status
What are the measures for different factors that can be used in a cohort study design?
compare incidence in exposed vs. non-exposed in the future
BEST measure of RR (strength of association)
What are the advantages of a cohort study?
directly measures incidence
(good for looking at rare exposures or risk factors)
look at multiple diseases (outcomes) for a selected risk factor
stronger measure of RR (risk factor precedes disease)
What are the disadvantages of a cohort study?
Very $$$
long time
Follow-up difficult
large # needed for rare dz
Ethical considerations
What is the % of increase in risk for a factor if the RR=4.2?
320%
% increase= (RR-1) x 100
If a risk factor is protective RR=0.57, then what is the % decrease in risk?
43%
% decrease= (1-RR) x 100
Given a group of diseases animals, we retrospectively compared diseased animals to a similar group to healthy animals.
Case-control study
What measure of the strength of the association can be made in a case-control study?
Odds ratio
What are the advantages of a case-control study?
less $$
quicker
fewer subjects needed
no risk to the animals
Which is better for a rare disease (case-control or cohort)?
case-control
What are the disadvantages of a case-control study?
careful selection of a control population (BIAS)
historical risk factors - difficult to verify & must be remembered
incidence cannot be determined***
