Evidence Based Medicine - Fundamentals Flashcards
What is evidence based medicine? definition
Evidence based medicine is the conscientious, explicit, and judicious
use of current best evidence in making decisions about the care of
individual patients. (Sackett DL et al, 1996)
What are the 5 steps to evidence based practice?
1: ask a question
2: find best evidence
3: evaluate evidence
4: apply information in combination with clinical experience + patient values
5: reflect + evaluate outcome
Why use evidence based medicine?
- ensure medicine sold are high quality, safe and efficient
What are the five sources of evidence + their levels?
level 1: randomised controlled trial
level 2: cohort studies
level 3: case controlled studies
level 4: case report or case series
level 5: animal and laboratory studies
What are some examples of study designs?
- experimental
- observational
What are types of experimental study designs?
*animal and laboratory studies
*clinical trials
- controlled trials e.g RCT
- uncontrolled trials
What are types of observational study designs?
*Cohort studies
* Case-controlled studies
* cross-sectional studies
What are the disadvantages of animal and lab study?
- Its application is limited considering the difference between human and animal
physiology - Experiments are undertaken in a highly controlled environment
What is a cross-sectional study?
- An observational study design where outcomes and exposures are
measured concurrently. - Participants are selected based on set inclusion and exclusion
criteria
(population based research)
What are the advantages to case-control study designs?
- Less expensive
- Easier to do and take less time
- Useful when obtaining follow-up data that is difficult to obtain due to the
nature of population being studied - More efficient if the disease is rare
- This design may be the only ethical way to evaluate something
What are the disadvantages to case-control study designs?
- Potential recall bias
- Subject to selection bias
- Generally do not allow investigators to calculate an incidence or absolute risk
What are the advantages to the cohort study?
- Can more clearly show the time of exposure and development of the outcome
because the subjects are without the disease at baseline. - Allows for evaluation of more than one outcome as it relates to an exposure
- Allows for the calculation of the incidence
What are the disadvantages to the cohort study?
*can be expensive and time consuming because of needing to follow a large number of people
*loss of follow up can begin to introduce bias
* may not be good for rare diseases
What are the advantages to the randomised controlled trial?
- Considered the gold standard
- This design allows for washout of most population bias
- Reduced influence by confounders
- Reduced variability in the outcome(s)
- Easier to blind patients than observational studies
What are the disadvantages to the randomised controlled trial?
- Generally more time consuming
- Tend to be more expensive
What are the advantages of the systematic review?
- Use strategies that reduce biases and
random errors. - Provide reliable information about the
topic being studied - Identify gap in knowledge to direct
future research
What is the disadvantage to the systematic review?
*Does not allow further analysis of data
What is the advantage and disadvantage to meta-analysis?
advantage: Objective evaluation of research findings
disadvantage: Not all topics have sufficient research evidence to allow a meta-analysis to be conducted
What are the advantages to guide-lines?
- Are on topic of relevance to population (usually determined by NHS England
or the Department of Health and Social Care). - Thorough and transparent development process to ensure fairness.
- Representative stakeholders involved in the process.
- Guidelines are developed using thorough literature reviews of many RCTs and
other forms of evidence. - Directly applicable to patients.
- Often take into account a huge number of potential treatments and drug
classes, e.g. type 2 diabetes guidelines. - Complex issues simplified.
- Regularly reviewed.
- Take into account cost considerations
What are the disadvantages to guide-lines?
*resources
*conflict of interest
What is an endpoint?
- An endpoint is an event or outcome that can be objectively measured in a study.
- Endpoints should be pre-defined and, ideally, sufficiently powered
What is the primary endpoint?
*main outcome to identify effectiveness of intervention
- needs to be clinically relevant
What is the secondary endpoint?
not the main outcome but additional events of interest, that the case study may not be specifically out to asses
What is a POE? (patient oriented end point)
An ideal endpoint should be a valid and applicable measure of how a
patient feels, functions or survives.
What are the advantages to POEs?
measures of true patient benefit, clinically meaningful, clinical
certainty
What are the disadvantages to POEs?
need large sample size, longer trial duration, more
expensive, delay in potentially beneficial medicines coming to market
What is a DOEs? (disease oriented endpoint)
also known as “surrogate” endpoints: do not directly measure how
a person feels, functions or survives, but which should be so closely
associated with a clinically meaningful endpoint that they are taken to be a
reliable substitute for them
What are the advantages to DOEs?
smaller sample size, shorter trial duration, less expensive,
expedites medicines to market.
What are the disadvantages to DOEs?
may not relate to clinically meaningful outcomes, may not
change at all stages of disease, may predict that harmful treatments are
effective.
What is ARR? (absolute risk reduction)
ARR: the straightforward difference between event rates.
ARR=Risk in the Control Group−Risk in the T
reatment Group
What is RRR? (relative risk reduction)
RRR: the difference in event rates expressed relative to what you started with
What is the RRR equation?
RRR = (risk in control group-risk in the treatment group / risk in control group) x100%
What is NNT? (number needed to treat)
The number of patients who need to receive a specific treatment over a defined period to prevent one additional adverse outcome (or
to achieve one additional positive outcome) compared to a control group or an alternative
treatment
What is the formula to calculate NNT?
NNT = 1/ absolute risk reduction (ARR)
