Types Of Studies Flashcards
(23 cards)
Types of studies
- case control
- cohort - prospective or retrospective
- randomised control trial
- cross sectional
Outline a case control study
- compares two groups
- group who have certain outcome - cases
- group without the outcome - control
- looks back retrospectively at assess exposure
- measures the odds ratio
What is a case control study useful for?
- studying rare diseases or outcome
- investigating associations between exposures and outcome
Disadvantages of case control study
- Vulnerable to recall and selection bias
- prone to confounding
Outline prospective cohort study
- starts with a group who are free from the outcome being studied
- follows them over time
- recording exposure status + tracking occurrence of outcome
Advantages + disadvantages of prospective cohort study
Pros:
- allows for direct measurement of exposure before the outcome develops
- minimises recall bias
.
Cons:
- time consuming + expensive due to long follow up periods
- loss to follow up
Outline retrospective cohort study`
- identifies individuals with the outcome of interest
- looks back to assess their exposure status by examining records + asking participants to recall past exposure
Advantages + disadvantages of retrospective cohort study
Pros:
- reduced loss to follow up then prospective cohort
- more efficient + cost effective than prospective studies
- useful for studying outcomes with long latency periods
.
Cons:
- prone to recall bias
- cannot establish temporal sequence
Outline a randomised control trial
- Assigns participants randomly to receive an intervention (treatment) or control (placebo or standard treatment)
- follows them prospectively to assess outcomes
Advantages + disadvantages of randomised control trails
Pros:
- reduces confounding
- gold standard for assessing efficacy + safety of interventions
.
Cons:
- expensive + time consuming
- may not always be feasible or ethical
Outline a cross sectional study
Collects data from population at a single point in time to assess the prevalence of an outcome + the distribution of exposures
Uses of cross sectional studies
Generating hypotheses + estimating prevalence
Outline a pragmatic trial
- intention to treat analysis
- analyses according to original allocation regardless of completion of follow up or adherence
- perseveres randomisation > minimises confounding
- reduces bias due to loss of follow up
Reason for doing intention to treat analysis
- preserves randomisation > minimises confounding
- reduces bias due to loss of follow up
Outline explanatory trail
- per-protocol analysis
- analyses only those who completed follow up + adhered to treatments
- loses effects of randomisation > may introduce confounding
Levels of evidence
- Ia: from meta-analysis of randomised control trials
- Ib: from at least one randomised control trial
- IIa: from at least one well designed controlled trial but not randomised
- IIb: from at least one well designed experimental trial
- III: from case, correlation + comparative studies
- IV: from a panel of experts
Reliability in statistics
To imply consistency of measure
Validity in statistics
Whether a test accurately measures what it is supposed to measure
Reliability vs validity
Reliability - consistency
Validity - accuracy
What is power of a study?
Probability of correctly rejecting the null hypothesis when it is false
What is power of a study influenced by?
- sample size
- significance level
- meaningful effects size
Incidence defintion
The number of NEW cases per population in a given time period
Prevalence definition
Number of ALL cases in a given time per (divided by) population
