Evidence Based Dentistry Flashcards
(27 cards)
Definition of risk
The chance of something happening
Definition of outcome
Something that might happen
Definition of statistics
Numbers that summarise information; based on observations of large numbers
Risk calculation
(%) = no. of events of interest / total no. of events (x100)
Odds calculation
Number of events of interest / number without event of interest
Definition of absolute risk difference (ARD)
ARD - difference in risk between groups.
Definition of value of no difference
When ARD = 0 and/or RR = 1 and/or OR = 1 and there is no risk/benefit to one group
Definition of number needed to treat (NNT)
NNT= 1/ARD - number of patients required to prevent one patient developing outcome
NNT for statins
33
Definition of relative risk (RR)/risk ratio
Measure of likeliness of event in one group compared to another
Relative risk calculation
Calculate risk % in Tx and control groups; divide Tx by control group
Odds ratio calculation
Odds in Tx group / control group (number of events / number with no event)
Definition of confidence interval
Range of values that a population treatment is likely to lie in
How can confidence intervals be used to identify a difference between treatment and control groups (2)
A CI that straddles/overlaps the value of no difference indicates insufficient evidence for a difference
A CI that does not overlap/straddle the value of no difference indicates sufficient evidence for a difference
A wide confidence interval may be due to
Small sample size
Definition of case report/series
Report on a single patient with an outcome of interest
Advantages (2) and disadvantages (2) of case report/series
Identifies new disease outcomes and generates hypotheses
Lack of control and no valid statistics
Definition of cross-sectional study
Observation of a defined population at a simple point in time. Determines exposure and outcome at the same time
Advantages (2) and disadvantages (3) of cross-sectional study
Estimates prevalence and can investigate risk factors
Causality, confounding bias and recall bias
Definition of cohort study
Measures exposure of an established group of individuals within a population. Follow up over a period of time and identifies outcomes of interest
Advantages (4) and disadvantages (6) of cohort study
Estimates incidence and causes, prognosis and direction of events
Difficult identifying controls, confounding bias, blinding difficulties, expensive, time consuming and requires large numbers
Definition of randomised control trial (RCT)
Gold standard design for effectiveness and efficacy
Four design elements of a randomised control trial with examples (4)
Specification of participants (inclusion/exclusion criteria)
Control (existence of comparison group)
Randomisation (allocation of treatments to participants - minimise bias)
Blinding/masking (preventing anyone/everyone from knowing who is receiving what treatment)
Benefit of allocation concealment
Prevents selection bias by concealing allocation sequence from those assigning participants to intervention groups until moment of assignment
