List the types of bias.
Types of bias:
1 - Selection:
2 - Performance
3 - Allocation
4 - Information:
5 - Review
6 - Verification
7 - Attrition
8 - Publication
9 - Spectrum
10 - Contamination
11 - Confounding (a variable that influences both the dependent and independent variable, and can therefore cause or prevent the outcome of interest).
12 - Confirmation (no extra card on this - bias that occurs when more weight is given to evidence that confirms the researchers’ beliefs, and undervalues evidence that could disprove it).
Define selection bias.
Selection bias is bias that occurs when groups in a study differ systematically from the population of interest.
It comprises 3 subtypes:
1 - Sampling bias is bias that occurs due to differences in sampling probability amongst eligible participants.
2 - Response bias is bias that occurs when non-responders differ to responders.
3 - Healthy worker / reproducer bias is bias that arises from the tendency of a study population to be healthier than the population of interest.
Define performance bias.
Performance bias is bias that occurs due to systematic differences between the amount of attention received from researchers, or exposure to factors other than the intervention of interest, between groups.
Define allocation bias.
Allocation bias is bias that occurs due to systematic differences in how participants are assigned to treatment and control groups.
Define information bias.
Information bias is bias that occurs due to systematic differences in how outcomes are measured in treatment and control groups.
It comprises 5 subtypes:
1 - Recall bias is bias that occurs when participants in a study are more or less likely to accurately recall information regarding their exposure depending on their outcome, or vice versa.
2 - Recording bias is bias that occurs due to differences in the level of availability of medical information between groups with and without an outcome or exposure of interest.
3 - Interviewer bias is bias that occurs due to distortion of the response given by an interviewee due to preconceived judgement on behalf of the interviewer.
4 - Lost to follow-up bias is bias that occurs due to differences between individuals that are lost to follow-up and those that are successfully followed-up (similar to attrition bias).
5 - Social acceptability bias is bias that occurs due to the tendency of participants to answer questions in a manner that will be viewed favourably by others.
Define verification bias.
What is the difference between partial and differential verification bias, and how do they impact on the results?
Define attrition bias.
Attrition bias is bias that occurs due to differences in the number and type of participants that are lost from different groups.
Define publication bias.
Publication bias is bias that occurs when the outcome of research affects its likelihood of being published.
Define spectrum bias.
Spectrum bias is bias that occurs when a diagnostic test is studied in a group that is different to the population for which the test is designed.
*Don’t forget to also check disease status as well as other baseline characteristics.
Define contamination bias.
Contamination bias is bias that occurs when members of the control group are inadvertently exposed to the intervention.
What are the two overarching categories of epidemiological study?
What is the difference between these study types?
List all of the subtypes of epidemiological study and state whether they are descriptive or analytic.
Types of epidemiological study:
Mixed (descriptive or analytic):
1 - Ecological study.
2 - Cross-sectional study.
Descriptive:
1 - Case report.
Analytic:
1 - Cohort study.
2 - Case-control study.
3 - Clinical trial.
What is an ecological study?
How is this study design useful?
What is a case report?
A case report is a type of descriptive study that illustrates novel or atypical features identified in clinical practice.
What is a cross-sectional study?
What are its advantages and disadvantages?
Advantages:
1 - Inexpensive.
2 - Quick.
Disadvantages:
1 - It is hard to make causal inferences from cross-sectional data since the time sequence of exposure and outcome cannot be assessed.
2 - It is difficult to establish a true association with age since individuals born in different years may have had different exposure experiences as they age.
3 - It is only possible to analyse prevalent cases in cross-sectional studies (also true for case-control studies). Prevalent cases include a mixture of incidence and survival, meaning they include factors that determine duration of illness.
What is a cohort study?
What are its advantages and disadvantages?
Followed-up over time to determine who develops the outcome of interest (prospective), or
Already followed-up and are assessed on the basis of their outcome (retrospective).
Advantages:
1 - Cohort studies are useful for following-up rare exposures.
2 - Cohort studies are effective in establishing cause and effect since exposure is measured before disease occurrence.
3 - There is no limit to the number of diseases for which the risk of occurrence may be related to the exposure.
4 - Cohort studies are able to make use of incident cases, which are preferable to prevalent cases (because prevalent cases include a mixture of incidence and survival, meaning they include factors that determine duration of illness).
5 - Cohort studies can eliminate recall bias if exposure is ascertained from another source (such as medical records) at the start of the study.
Disadvantages:
1 - Cohort studies are not useful for studying rare diseases because few participants will develop the disease.
2 - Cohort studies involve large numbers of people over long periods of time and so are expensive and logistically difficult.
3 - Cohort studies are limited to studying one exposure.
What is a case-control study?
What is a nested case-control study?
What are the advantages and disadvantages of a case-control study?
1 - The cases are nested within a well-defined cohort (ideally population-based), for which the level of ascertainment of the cases is known to be very high.
2 - A specified number of controls is matched to each case. This leads to a minor loss in statistical efficiency but significantly reduces cost and streamlines data analysis.
Advantages of case-control studies:
1 - Case-control studies are useful for studying rare diseases.
2 - There is no limit to the number of exposures that can be related to the risk of occurrence of the outcome.
Disadvantages of case-control studies:
1 - Case-control studies are prone to recall bias as they may require the participants to recall information regarding previous exposure.
2 - Case-control studies are limited to studying a single disease at a time.
3 - It is only possible to analyse prevalent cases in cross-sectional studies (also true for cross-sectional studies). Prevalent cases include a mixture of incidence and survival, meaning they include factors that determine duration of illness.
What is a clinical trial?
List 4 key features of clinical trials.
What are its advantages and disadvantages?
1 - Randomisation (if it is a randomised control trial).
2 - Concealment of allocation.
3 - Blinding.
4 - Intention to treat (ITT) analysis.
Advantages:
1 - Produces the strongest empirical evidence from which to make causal inferences.
2 - Can minimise sources of bias and confounding if performed correctly.
Disadvantages:
1 - Logistically difficult and expensive to carry out owing to its prospective design and often large sample size.
2 - Ethical requirement for equipoise (the assumption that it is unknown as to whether the intervention would favourably affect the outcome of either the control or experimental group).
Define review bias.
What type of data are most prone to review bias?
List the Bradford-Hills criteria for causation.
Bradford-Hills criteria for causation:
1 - Biological plausibility
2 - Time
3 - Strength of association
4 - Dose-response relationship / biological gradient
5 - Consistency
6 - Specificity
7 - Coherence
8 - Experiments
9 - Analogy
What is I squared?
I squared measures the degree of inconsistency across studies in a meta-analysis that is not accountable by chance.
*A measure of heterogeneity
What is incidence, point prevalence, period prevalence, absolute risk, attributable risk (AKA risk difference), relative risk and odds ratio?
How can confounding factors be adjusted for in statistical analysis?
Adjustment for confounding can be achieved through the use of a suitable regression model:
What is reflexivity?
Reflexivity is the process of a researcher critically examining the potential influence of their professional background, experience and personality on: