hierarchy of evidence
1) Meta-analysis/ Systematic Review
2) RCT
3) Cohort
4) Case control
5) Cross sectional
6) Case series (collection of similar cases)
Meta analysis definiton
An overview of a topic in which the results of all of the included studies are similar enough statistically that the results are combined and analysed as if it were one study.
A meta-analysis uses the quantitative results from the individual studies, pools them together using a statistical method, and produces a new single quantitative result. This new quantitative result is known as the ‘pooled treatment result’and is depicted graphically in a forest plot
Systematic review definition
An overview of primary research on a particular research question that tries to identify, select and appraises all relevant high quality evidence to answer the research question
A disadvantage of meta-analysis & systematic reviews
Relies on published studies –> publication bias
RCT definition
Cohort study
• People are randomly allocated to a treatment or control group
5 advantages of RCTs
- Studies effect
- Has a control group (balances the confounders)
- Randomised
- Powered for analysis
- Blinding
5 disadvantages of RCTs
• Expensive • Time consuming • Volunteer bias • Not realistic clinical practice (e.g frequent follow-ups) • Can be ethically problematic
Cohort study defintion
Longitudinal observational study - follows people with a common exposure (e.g smoking) over time to determine the risk of subsequent disease
5 advantages of Cohort studies
- Studies risk factors (for common outcomes)
- Safe (ethics)
- Match characteristics
- Realistic patients
- Establish timing & directionality of events
5 disadvantages of Cohort studies
• Cannot blind (difficult) • Loss in follow-up (attrition bias) • Expensive • Hidden confounder • Requires large sample sizes or long follow-up for rare diseases
Case control definition
Identifies two groups (with and w/o disease) and looks back for contributing factors
4 advantages of case control studies
- Studies rare outcomes & disorders
- Small sample size required
- Quick & Cheap
- Safe (ethics)
3 disadvantages of case control studies
- Recall bias (retrospective study)
- Selection bias
- Difficult to select control groups
Cross-sectional study defintion
Descriptive study
• ‘Snapshot’ of a population at a given time in which disease and exposure status are measured at the same time
2 advantages of cross-sectional studies
- Quick & Cheap
* Safe (ethics)
4 disadvantages of cross-sectional studies
- Association not causation
- Recall bias
- Unequal group sizes
- Unequal distribution of confounders
Case series definition
Collection of similar cases from a hospital or healthcare professional
What is audit?
Review of (current) practice against a set standard
What is research?
Study trying to find out what we should be doing with an aim to advance medical studies or protocols and procedures
What is quality improvement?
A process by which we achieve better patient experience and outcomes
What is research governance?
The range of regulations, principles and standards of good practice which ensure high quality research
How is risk and risk ratio (same as relative risk) calculated?
AR = Absolute risk (No of events / no of people)
Risk ratio = (AR in treatment group/ AR in control group)
What does a risk ratio of 1 (or CI including 1) mean?
No significant difference between intervention and control
What does a risk ratio of 2 mean?
Events are two times MORE likely in the treatment group than the control group
