Study Designs Flashcards
What is the difference between experimental and observational study designs?
Experimental- exposure is assigned by investigator.
Observational- exposure not assigned
What type of studies are analytical and descriptive studies?
Observational
What is the difference between analytical and descriptive studies?
Analytical studies have a control/comparison group, while descriptve studies do not.
What are the advantages and disadvantages of observational studies?
Advantages: - used to generate hypotheses - can be the first observation of a rare occurrence Disadvantages: - Lowest level of evidence - No comparison group
What is a case study and when is it used?
Detailed report by a health professional of a single patient.
Used for adverse effects and rare events
What is a case series?
Advantages: - Identification of rare disease and exposures - Generates hypotheses Disadvantages - Selection bias - Confounders
What are ecological studies?
Observational descriptive studies of populations or groups (rather than individuals).
Compare disease frequencies between different populations and different times.
What are the advantages and disadvantages of ecological studies?
Advantages:
- Fast, cheap, easy
- Hypothesis generating
Disadvantages:
- Highly susceptible to bias and confounders.
- Only associations can be drawn and not causation
- May confuse characteristics of a group for characteristics of an individual.
What is a cross-sectional study?
Asses the exposure and outcome at the same time and the direction of the relationship cannot be determined.
Measures the presence/absence of a disease and prevalence of a disease.
What are the advantages and disadvantages of cross-sectional studies?
Advantages: - Cheap, easy - Prevalence estimated - Useful for understanding etiology - Hypothesis generating. Disadvantages: - Cannot infer causation - Snapshot only and so results depend on time frame.
What are case-control studies?
Retrospective study in which data on exposures is collected in one point in time and exposures are collected at a previous point in time.
Compares the occurrence of possible cause in cases and control.
Odds ratios are used.
What are the advantages and disadvantages of a case-control study?
Advantages:
- Good for rare and long outcomes/disease
- Cheap, fast (2-3 years), easy.
Limitations:
- Control selection
- Through elimination of confounders, exposures may be eliminated
- High probability of recall bias
- High probability of selection bias as disease is known to researcher
- Measurement error
- Cannot estimate the incidence.
What is a cohort study?
The incidence of an outcome between those exposed and not exposed to a risk factor during the study time.
On what basis are participants selected in a case-control study?
Base on the presence/absence of outcome.
On what basis are participants selected for a cohort study?
Based on exposure to a risk factor.
What are the advantages and disadvantages of cohort studies?
Advantages:
- Identifies the natural history of the disorder
- Identifies the temporal sequence between exposure and outcome
- Good for rare exposures and common outcomes
- Very rigorous experimental design.
Disadvantages:
- Selection bias
- Confounders arise from individual participant differences
- Insufficient to study rare diseases
- Loss to follow-up
- Expensive and time-consuming.
What are randomised control trials?
Subjects are randomly allocated to intervention/control group and the outcomes of the two treatments are compared.
What does randomisation is and RCT aim to achieve?
The two groups being a similar and possible.
What is a community trial?
RCT at a group, rather than individual level.
What is a meta analysis?
Comparison of separate similar studies.
Which study designs allow investigation of rare disease?
Ecological, case-control, case studies.
Which study designs do not allow study of rare disease?
Cross-sectional and cohort.
Which study design allows investigation of rare causes?
Cohort study design.
Which study design allows testing of multiple outcomes from a single exposure?
Cohort
Which study designs allow study of multiple exposures?
Case-control and cohort.
Which study design allows assessment of a time relationship?
Cohort, RCT
Which study designs allow direct measurement of incidence?
Cohort, RCT
Which study design involves investigation of long, latent periods?
Case-control.
What is a randomised control trial?
A prospective study in which participants have an equal chance of being part of the control or experimental group.
Why does blinding occur in RCTs?
To avoid performance bias (placebo effect).
What are the advantages of RCTs?
- Lowest risk of all four biases and confounders
- Demonstrates strong causal relationship
- Measure multiple outcomes
- Measure incidence
What are the limitations of RCTs?
- Expensive
- Long follow-up periods
- Ethical issues (deception when using placebos).
What is a cross-over trial?
Perform a randomised control trial then, following a washout period, cross the two over swapping over the intervention.
What are the advantages and disadvantages of a cross over RCT?
Advantages: - Increases sample size - Eliminates individual participant differences Disadvantages: - Order effects.
What is a N of 1 RCT?
A single case is the participant of the trial: trial, washout period, different trial
What is a systematic review?
Overview of medical literature with reproducible objectives and methodology
