Study Design Flashcards
What happens in a randomised controlled trial?
Participants randomly allocated to intervention or control group (e.g. standard treatment or placebo).
What may limit the use of a randomised controlled trial?
Practical or ethical problems
What happens in a cohort study?
Observational and prospective.
Two (or more) are selected according to their exposure to a particular agent (e.g. medicine, toxin) and followed up to see how many develop a disease or other outcome.
What is the usual outcome measure in a cohort study?
Relative risk
What are participants selected according to in a cohort study?
Their exposure to a particular agent
What happens in a case-control study?
Observational and retrospective.
Patients with a particular condition (cases) are identified and matched with controls.
Data is then collected on past exposure to a possible causal agent for the condition.
What is the usual outcome measure in a case-control study?
The odds ratio
Benefits of a case-control study?
1) Inexpensive, produce quick results
2) Useful for studying rare conditions
Key disadvantage of a case-control study?
Prone to confounding
What is confounding?
when a third variable (a confounder), distorts the relationship between an exposure and an outcome
What happens in a cross-sectional survey?
Provide a ‘snapshot’, sometimes called prevalence studies
Disadvantage of a cross-sectional survey?
Provide weak evidence of cause and effect
What are 3 common causes of confounding?
Age, sex and social class
Confounding occurs when there is a non random distribution of risk factors in the populations
In the design stage of an experiment, what can confounding be controlled by?
Randomisation –> aims to produce an even amount of potential risk factors in two populations.
In the analysis stage of an experiment, what can confounding be controlled for by?
Stratification
Clinical trials are commonly classified into how many phases?
4 - (0, I, II, III, IV)
What is the goal of phase 0 of a clinical trial?
Exploratory studies
What happens in phase 0 of a clinical trial?
Involves a very small number of participants and aim to assess how a drug behaves in the human body.
Used to assess pharmacokinetics and pharmacodynamics.
Phase 0 trials help in determining whether it is FEASIBLE to move on to further phases.
What is the goal of phase I of a clinical trial?
Safety assessment
What happens in phase I?
Determines side-effects prior to larger studies.
Conducted on healthy volunteers
What is the goal of phase II of a clinical trial?
Assess efficacy
What happens in phase II of a clinical trial?
Involves small number of patients affected by particular disease
May be subdivided into:
- IIa - assesses optimal dosing
- IIb - assesses efficacy
What is the goal of phase III of a clinical trial?
Assess effectiveness
What happens in phase III of a clinical trial?
Typically involves 100-1000’s of people, often as part of a randomised controlled trial, comparing new treatment with established treatments
What is the goal of phase IV of a clinical trial?
Postmarketing surveillance
What happens in phase IV?
Monitors for long-term effectiveness and side-effects
Which type of study follows a group of people over time to determine how many develop a specific health outcome (prospective)?
Cohort
What type of study compares two groups of people to determine if an exposure is a risk factor for a health outcome (retrospective)?
Case control
Efficacy vs effectiveness?
Efficacy is how well an intervention performs under controlled conditions, while effectiveness is how well it performs in the real world.
