evidence based dentistry Flashcards
What is the numerator and the denominator?
Numerator - number of people who actually experience the outcome
Demominator - number of people who could potentially experience the outcome
What is the relative risk reduction?
The decrease of percentages risk as a number
Eg - 4.9% down to 0.8% is an 84% decrease
What is the absolute risk reduction?
How many percent the decrease was by
Eg - 4.9% down to 0.8% is a 4.1% decrease
What is NNT and how is it calculated?
Number needed to treat
The number of people needed to treat to prevent developing the issue in 1 patient
1/absolute risk difference
What is the risk ratio and how is it calculated?
How many times more likely is person in exposure group likely to experience results
Risk in exposure group/risk in placebo group
How is the odds ratio calculated?
Odds of both divided
(%/1-%)
What are confidence intervals?
The range of values the absolute risk difference will take in the population
If repeated on different groups it should give the same results
Shouldn’t overlap 1
Describe CI for a difference between 2 quantities
If 2 values are equal, the difference is 0
The value of no difference is 0
There is sufficient evidence for a difference between 2 values in the population if the CI for the difference does not overlap 0
Describe CI for a ratio between 2 quantities
If 2 values are equal, the ratio is 1
The value of no difference is 1
There is sufficient evidence for a difference between 2 values in the population if the CI for the ratio does not overlap 1
What are observational uncontrolled studies?
Researchers watch what happens to a group of people
Eg - group of pts with disease X are treated with drug Y
What are controlled studies?
Can be cohort or case control
Researchers observe what happens to people in different situations without intervening
What are case report/case series studies?
Report on single patient or series of pts with an outcome of interest - no control group involved
What are case report/case series studies used for and what are the disadvantages?
Used to identify new disease outcome and hypothesis generation
Disadvantages - can’t demonstrate valid statistical associations and lacks control group
What are cross sectional studies?
Observation of defined population at single point in time or time interval
Exposure and outcome determined at same time
What are cross sectional studies used for and what are the disadvantages?
Investigating prevalence of disease and potential risk factors
Disadvantages - causality, confounding and recall bias
What are case control studies?
Study of people with a disease and a suitable control group of people without the disease
Looks back in time at exposure to particular risk factors in both groups
What are case control studies used for and what are the disadvantages?
Looking at potential causes of disease
Disadvantages - confounding, recall bias, selection of controls, time relationship
What are Cohort studies?
Establish group of individuals in population (measures exposure)
Follow up over a period of time
Identify those that develop disease (outcome of interest)
What are Cohort studies used for?
Estimating incidence of disease
Investigating causes of disease
Determining prognosis
Timing and direction of events
What are the disadvantages of cohort studies?
Controls difficult to identify
Confounding
Blinding difficult
In rare diseases - need large samples
Expensive and time consuming
What are RCTs?
Pts randomly split into 2 groups - one gets intervention, the other gets placebo
Gold standard for effectiveness and efficacy
Useful for clinical studies
Provides strong evidence on effectiveness of treatments
List 4 design elements of RCTs
Specification of participants - inclusion and exclusion criteria
Control groups
Randomisation
Blinding/masking - neither participants or researchers know who received which treatment
List 2 inclusion or exclusion criteria
Age
Diagnosis or severity of disease
Name an advantage of RCTs
Strongest evidence for causality
What are the disadvantages of RCTs?
More difficult to design and conduct than observational studies
Still same risk for bias
Not suitable for all research questions
What does PICO stand for?
Population
Intervention
Comparison
Outcome
What are systematic reviews?
Literature review that uses systematic methods to collect secondary data, critically appraise research studies and synthesise studies
What are the advantages of systematic reviews?
Can tell if we have a conclusive answer or if more research is needed
Saves readers time bringing a body of literature together
Unbiased reliable evidence
Resolves inconsistencies
Helps identifies gaps where good studies are not available
Identifies when questions have been fully answered
What are the steps of a systematic review?
Well formulated question
Comprehensive data search
Unbiased selection
Assessment of papers
Synthesis of data
How are statistically significant positive results often biased?
More likely to be published - publication bias
More likely to be published quickly - time lag bias
More likely to be published in English - language bias
More likely to be cited by others - citation bias
What are meta-analyses?
Using statistical methods to combine the results of different studies
What are the different data types in a meta-analysis?
Dichotomous - yes or no
Continuous - bp, weight
What are the different types of heterogeneity?
Clinical - variation in participants, interventions, outcomes
Methodological - variation in methods used in studies
Statistical - variation in treatment effects above that expected by chance
What is the Chi-squared test?
Tests for heterogeneity
If P <0.1, this demonstrates significant heterogeneity and may not be appropriate to pool data
I squared is the percentage variation due to heterogeneity rather than chance (<50% is acceptable)
What is used to evaluate bodies of evidence?
GRADE
Grading of
Recommendations Assessment,
Development and
Evaluation
What can lower the quality of a body of evidence?
High or unclear risk of bias
Inconsistency between studies - heterogeneity
Indirectness - studies not similar
Imprecision
Publication bias
What is the CASP tool?
Critical appraisal skills programme
Checklists to help evaluate research studies
