Evidence based medicine Flashcards
Define evidence based medicine.
The conscientious, explicit and judicious use of current best evidence in making decisions about the care of the individual patient. It means integrating individual clinical expertise with the best available external clinical evidence from systematic research.
What are the 5 steps of evidence based medicine?
Assess the patient
Ask the question
Acquire the evidence
Appraise the evidence
Apply your findings
What does the triad of implementing the practice of evidence based medicine consist of?
Individual clinical expertise
Best available clinical evidence
Patient expectations and values
Define clinical governance.
A system through which NHS organisations are accountable for continuously improving the quality of their services and safeguarding high standards of care by creating an environment in which excellence in clinical care will flourish.
What are the 6 main components/ domains of clinical governance?
Education + training
Clinical audit
Clinical effectiveness
Research + development
Openness
Risk management
What is an audit?
A quality improvement process that seeks to improve patient care and outcomes through systematic review of care against explicit criteria and the implementation of change.
What are the 5 steps in an audit cycle?
Identify a problem
Define criteria/ set standards
Observe current practice + collect data
Compare current performance against standards
Implement change
What are the 2 different types of medical study?
Observational studies
Experimental studies
What are the 4 types of observational study?
Cross-sectional studies
Cohort studies
Case-control studies
Ecological studies
What 2 factors are assessed simultaneously in cross-sectional studies?
Risk factors + presence of disease
What is a cross sectional study?
An observational study where data is collected about disease and risk factors simultaneously.
What are the advantages of cross-sectional studies?
-Quick
-Can study multiple outcomes/ exposures
-Can be sued to study conditions of long duration
What are the disadvantages of cross-sectional studies?
-Need large groups
-Sequence of events can remain unclear
-Conditions of short duration are hard to identify in a single study unless very common
What can cross-sectional studies be used for?
Assess prevalence
Identify causes of disease
Assess results of medical intervention
What is a cohort study?
A longitudinal observational study that follows a group of individuals forward in time to monitor effects of a proposed etiological factor on them
What is a population-based cohort study?
A cohort study that enrols individuals regardless of their exposure status (allows calculation of overall incidence in a population).
What are cohort studies used to assess?
Incidence of a disease
What are the advantages of cohort studies?
-Can assess a sequence fo events over time
-Used to study a wide range of exposures
-Can provide information on a wide range of outcomes
-Smaller risk of selection bis than a case-control study
What are the disadvantages of a cohort study?
Expensive
Long in duration
Loss to follow-up can be a problem
Disease aetiologies in populations can alter over time
What is a case-control study?
AN observational study where 2 groups fo patients (with or without disease) are compared on the basis of a proposed causative factor that occurred in the past.
What cannot be estimated from case-control studies?
Disease incidence of prevalence
What are 2 types of bias that can affect case-control studies?
Recall bias
Selection bias
What are advantages of a case-control study?
Inexpensive
Easy
Quick
What are disadvantages of a case-control study?
Recall bias
Selection bias
What are the disadvantages of an RCT?
- Not always ethical
- High dropout when intervention has undesirable effects
- Expensive
What are the advantages of an RCT?
- Causal inferences
- Randomisation minimises bias
- Tailored to a specific research question
What are the disadvantages of a systematic review?
- Researcher can only use published or readily available studies
- Conclusions may be unreliable
- Unpublished studies may be hard to find
- Results that are negative or inconclusive may remain unpublished
What are the advantages of a systematic review?
- All available evidence
- Published/Unpublished research
- Increased total sample size = certainty and precision
- Indicated heterogeneity
- Subgroup and sensitivity analyses
What is confounding?
Happens when a relationship between an exposure and an outcome is distorted by their shared relationship with another variable.
What can confounding result in?
-Observation of a difference between study populations when one does not exist
-Failure to observe a difference when one does exist
-Under or overestimation of an effect
What are the 2 most common ways that confounding can be accounted for the by a researcher?
Stratification
Multiple variable regression
How is stratification carried out?
- an analytical approach where exposure: outcome associations are categorised into different subgroups of the confounder.
- different subgroups are known as different strata.
How is multiple variable regression carried out?
Allows us to estimate the association between a given independent variable and the outcome holding all other variables constant.
It provides a way of adjusting for (or accounting for) potentially confounding variables that have been included in the model.
What is a benefit that multiple variable regression has over stratification?
Multiple variable regression can allow adjustment for multiple confounders at the same time.
What is bias?
The systematic introduction of error into a study that can distort the results in a non-random way.
What are the 4 main types of bias?
Selection
Performance
Measurement
Publication
Selection bias commonly occurs in which type of study?
Case-control
What is selection bias?
selecting participants for the study and assigning them to particular arms of the study.
**Bias introduced by the selection of individuals, groups or data for analysis in such a way that proper randomization is not achieved, thereby ensuring that the sample obtained is not representative of the population intended to be analyzed
What is attrition bias?
Occurs when those patients who are lost to follow-up differ in a systematic way to those who did return for assessment or clinic.
**Bias that arises from systematic differences in the way participants are lost from a study.
What is measurement bias?
Measurement bias refers to any systematic or non-random error that occurs in the collection of data in a study.
**when information is recorded in a distorted manner (e.g. an inaccurate measurement tool).
What is observer bias?
Occurs when variables are reported differently between assessors.
What is procedure bias?
Occurs when subjects in different arms of the study are treated differently (other than the exposure or intervention).
What is misclassification bias?
Occurs when a study participant is categorised into an incorrect category altering the observed association or research outcome of interest.
**Basically occurs when a variable is classified incorrectly.
What is information bias?
Information bias is any systematic difference from the truth that arises in the collection, recall, recording and handling of information in a study, including how missing data is dealt with.
**Happens when key information is either measured, collected, or interpreted inaccurately.
What is the way in which unknown confounders are dealt with in experimental studies?
Randomisation
How does randomisation work to reduce confounding?
By distributing characteristics of patients that may influence outcomes randomly between the groups.
What is allocation concealment?
A process that ensures that both clinicians and participants are unaware of the treatment being allocated prior to enrolment in the study.
What does the null hypothesis state?
That there is no statistical difference between two treatments being compared.
What is a primary end point in a study?
The main point of interest of the study in question.
What is a secondary end point?
Other characteristics that are measured in the study participants that help to answer other relevant questions (i.e. is a drug cost-effective?)
What is validity?
The extent to which a conclusion or measurement is well-founded and corresponds accurately to the real world.
What is internal validity?
The extent to which the methodology permits a conclusion about causal relationships to be made.
What is external validity?
The extent to which results of a study can be extrapolated to other situations and people.
A measure of how study findings apply to the wider population.
What is involved in the pre-clinical phase of research trials?
Research and then studies at cellular level/ animals.
What is involved in phase 1 of a clinical drug trial?
Small trials on healthy volunteers.
Used to gather information on dosing, timing and safety.
What is involved in phase 2 of a clinical drug trial?
What is involved in phase 3 of a clinical drug trial?
Several thousands of participants.
Evaluate the effectiveness of a new drug compares with existing drugs or placebo.
ARE GENERALLY RCTs.
What is involved in phase 4 of a clinical drug trial?
Post-marketing surveillance (designed to track long-term side effects and benefits).
What is post-marketing surveillance?
The practice of monitoring the safety of a drug within a patient population after it has been released.
What is meta-analysis?
A statistical procedure that integrates the results of multiple independent studies with common features with the goal of estimating the true common effect across these individual trials.
What does a meta-analysis increase?
Sample size and therefore statistical power.
What type of graph is normally used to display results in a meta-analysis?
Forest plot
What is a systematic review?
The first step in a meta-analysis where all articles relating to a research question are reviewed.
What type of graph is usually used in a systematic review?
Forest plot (no pooled results)
What does the area of a square on a forest plot represent?
The sample size
What do the horizontal lines on a forest plot represent?
The confidence interval.
What does the diamond on a forest plot represent?
The average effect size of the studies when combined.
Give the levels of evidence from bottom to top
5 - Expert opinions
4 - Case series (or poor quality cohort/ CC)
3b - Individual case control study
3a - systematic review of CC study
2c - outcomes research or ecological studies
2b - individual cohort studies or low quality RCTs
2a - Systematic reviews of cohort studies
1c - RCTs
1b - Indivisual RCTs with narrow CIs
1a - Systematic reviews of RCTs.
