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Flashcards in HaDPoP general Deck (29)
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What is a consensus useful for?

- Allocation of resources
- Projections of populations
- Trends in populations Eg Ethnicity or age


How are confidence intervals calculated?

Lower bound = Value ÷ Error factor

Upper bound = Value x error factor

(error factor equation given in exam)


Cohort studies can either be?

1) Prospective - disease free individual recruited and followed up

2) Retrospective - Disease free individuals recruited then exposure status calculated from historical documentation and followed up


Explain internal comparisons

Occur when you have sub-cohorts within your original group and then compare exposed and unexposed within the cohort



Explain external comparisons

Occur when you have your exposed population compared against a reference population instead

Use an SMR calculation (removes confounders)


Describe healthy worker effect

Healthy worker effect is whereby there is biasing of results when a study involves workers / employed individual compared ti a reference population and is a form of selection bias

When a comparison is made, it should always be against other working individuals to prevent any bias


Describe a case control study

A case-control study involves recruiting disease-free (controls) individuals and diseased individuals (cases) and then their exposure status is determined


What biases affect case-control studies?

- Selection bias
- Recall bias


What are the positives and negatives of a cohort study?

+ Good to study rare EXPOSURE; adequate numbers of people can be picked from the population, where a small number is exposed

+ Opportunity to look for different potential OUTCOMES at once from varying exposures

- Expensive and time consuming, especially if the disease has a long latent time period Eg AIDS

+ Allows for calculation of specific absolute risk


What are the positives and negatives of a case-control study?

+ Good for rare diseases; no need to follow thousands of individuals to get a few cases

+ Opportunity to look for different potential EXPOSURES at once, as long as detailed background can be obtained

+ Cheap and quick

- Can not obtain absolute risk (unless nested case-control)

- Heavily affected by recall and selection bias


Why do randomised controlled trials use randomisation?

Remove any confounders that may be present in the study, known or unknown


What is the Bradford-Hill Criteria used for?

To determine whether a causal-effect relationship has been established (once confounders, bias and chance have been removed), Bradford-Hill criteria can be used to evaluate the relationship

The more Bradford-Hill criteria present, the more likely it is to be a causal-effect relationship


What are the 9 Bradford-hill criteria

1) Strength of association

2) Specificity of association

3) Consistency of association

4) Temporal sequence

5) Dose response

6) Reversibility

7) Biological Plausibility

8) Coherence of theory

9) Analogy


Bradford-Hill criteria. Strength of association

Stronger associations (Eg high IRR or OR) are more likely to be causal


Bradford-Hill criteria. Specificity of association

Outcome is associated with a specific factor

Eg mesothelioma caused by asbestos exposure


Bradford-Hill criteria. Consistency of association

Association occurs in other studies too


Bradford-Hill criteria. Temporal sequence

Causative factor precedes the outcome


Bradford-Hill criteria. Dose response

Different levels of exposure lead to different levels of outcome

Eg radiation levels


Bradford-Hill criteria. Reversibility

Removal of causative factor causes reduced risk of outcome


Bradford-Hill criteria. Biological plausibility

Biological mechanism to support the theory


Bradford-Hill criteria. Coherence of theory

Observed observation confirms current scientific thinking


Bradford-Hill criteria. Analogy

Another similar disease has similar outcomes


Describe the ethics of a randomised control trial

Clinical Equipoise – Reasonable uncertainty into which drug is better for the patient, so not subjecting patients to known less effective treatment

Scientifically Robust – Persuit of knowledge for the good of the general population

Ethical Recruitment – Recruitment for region where drug will take affect and no unethical exclusions from the trial

Valid Consent – Participants given sufficient knowledge, cooling off period, chance to ask questions, and ability to withdraw from trial at any point

Voluntariness – No coercion or manipulation into entering the trial

+ The ethics of any medical roles


What is a systemic review?

A compilation of primary studies


What is a meta-analysis

Within a systemic review , a meta-analysis provide the quantitative synthesis of the primary studies used in the trial

provides an overall value with associated confidence intervals


What is a forest plot?

A graphical representation of a meta-analysis

The horizontal line corresponds to the 95% confidence interval

The Vertical line corresponds to "line of no effect"; intervention has no effect on the outcome

Overall effect is given to give best estimate of all the data analysed together


What two types of models can be used in a meta-analysis

1) Fixed effects model - assumes the studies used are homogenous and any variation between data comes from within-study variation

2) Random effects model - Assumes the studies are heterogenous and variation between data comes from within-study variation and between-study variation


In a funnel plot, what does a typical funnel shape indicate?

A well balanced systemic review


What are the advantages of a systemic review?

- Explicit methods can reduce bias and exclusion of poor quality studies

- Meta-analysis provides overall figure for the studies

- Large amounts of information can be assimilated quickly by healthcare professionals

- Reduction in time between research discovery and implementation of clinical use

- Used in Evidence-Based Practice guidelines