Evidence based medicine Flashcards
Define Evidence based medicine
The use of mathmatecal estimates of the risk of benefit and harm, derived from high quality research of population samples, to inform clinical descision-making in the diagnosis, investigation or managemnet of individual patients.
Describe the differences between observational and experimental studies
Observational studies are also called analytical studies, they can show and association between one variable and another and aim to identify causality.
Where as experimental studies (interventional studies are where a new treatment or intervention is trialed.
Name and describe the type of observational studies used
Cohort study- looks for causality
Case control stuyd- looks for causality
Cross-sectional/longitudinal studies- useful for looking at trends.
Define what bias is
Any trend in the collection, analysis, interpretation, publication or review of data that can lead to conclusions that are systemically different from the truth
This is a systematic deviation from the truth in one direction.
What is an error?
This is different from bias as errors occur randomly and bias is systematic
WHat is a confounding factor?
A factor that is associated with both the exposure of interets and the outcome of interest.
What is selection bias?
Sample does not represent population
What is detection bias?
Observations in treatment group pursued more than control group
What is observer bias?
Subjectivity of observer, variance in their decisions
What is recall bias?
Patients know which group they are in and may be more likely to report symptoms
What is response bias?
Patients enrolling themselves/self-selecting
What is publication bias?
Positive trials are more likely to be published.
Define incidence
The number of new cases of disease in a population, in a given time period, also known as the occurence rate. Usually reported as a percentage
Helps us to understand the risk of disease
Define prevelence
The total number of cases of a disease in a population, either in a time period or at a specific point in time.
Prevelence helps us to understand the burden of disease
What is a cohort study and when is it used?
A cohort of people are studied based on exposure and followed up to evaluate an outcome of interest.
The can be prospective or retrosepctive
Adv: incidence can be calculated in exposed and non-exposed individuals, multiple outcomes can be studied, bias less of an issue than in case-control studies
Disadv: requires large populations and take a long time (years) to do so are expensive
Explain what relative risk is
(outcome measure in cohort studies)
Risk in exposed group/ risk in unexposed group= RR
What is a case control study?
A comparision between individuals with a disease (outcome) of interest (cases) ad those without the disease of interest. The cases and controls are each assessed to determine if they have had exposure to the variable of interest.
Almost always retrospective
Adv: smaller sample sizes generally required, quicker reults, cheaper
Disadv: more prone to bias, can be difficult to prove causation, not possible to calcaulate incidence, selecting controls can be difficult, particulalry prone to recall bias
Define what odds ratio is
The ratio of odds of exposure of those with the outcome to those without the outcome
If it is 1 this suggests there is no difference is odds of exposure between the 2 groups
What is a cross-sectional study?
Looks at the outcome and exposure in a ppulation or an individual at a specific point in time- they look at a cross section of society.
If a cross sectional study is repeated multiple time in succession then this is a longitudinal study.
They both look at trends in a population. The CAN’T look for causality.
Give examples of types of intervention trails
The randomised controlled trail (RCT)- this is the gold standard, these have little chance of bias but are time consuming and expensive
What does single blind mean?
Patients don’t know which treatment they are taking (e.g. in an RCT)
What does double blind mean?
Neither the patients or the clinical/scientists involved in alaysis know which treatments they are on.
What is a systematic review?
A review of a clearly formulated question that used systematic methods to identify, select and critically appraise relevant research and to collect and analyse data from the studies that are included in the review.
What is meta-analysis?
The data/statistical part of a systematic review. Pulls together data from individual studies and analyses this. The data is usually presented in a forest plot.
You can have a systematic review without a meta-analysis.
