evidence based dentistry

Question 1

What is the numerator and the denominator?

Answer 1

Numerator - number of people who actually experience the outcome
Demominator - number of people who could potentially experience the outcome

Question 2

What is the relative risk reduction?

Answer 2

The decrease of percentages risk as a number
Eg - 4.9% down to 0.8% is an 84% decrease

Question 3

What is the absolute risk reduction?

Answer 3

How many percent the decrease was by
Eg - 4.9% down to 0.8% is a 4.1% decrease

Question 4

What is NNT and how is it calculated?

Answer 4

Number needed to treat
The number of people needed to treat to prevent developing the issue in 1 patient
1/absolute risk difference

Question 5

What is the risk ratio and how is it calculated?

Answer 5

How many times more likely is person in exposure group likely to experience results
Risk in exposure group/risk in placebo group

Question 6

How is the odds ratio calculated?

Answer 6

Odds of both divided
(%/1-%)

Question 7

What are confidence intervals?

Answer 7

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

Question 8

Describe CI for a difference between 2 quantities

Answer 8

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

Question 9

Describe CI for a ratio between 2 quantities

Answer 9

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

Question 10

What are observational uncontrolled studies?

Answer 10

Researchers watch what happens to a group of people
Eg - group of pts with disease X are treated with drug Y

Question 11

What are controlled studies?

Answer 11

Can be cohort or case control
Researchers observe what happens to people in different situations without intervening

Question 12

What are case report/case series studies?

Answer 12

Report on single patient or series of pts with an outcome of interest - no control group involved

Question 13

What are case report/case series studies used for and what are the disadvantages?

Answer 13

Used to identify new disease outcome and hypothesis generation
Disadvantages - can’t demonstrate valid statistical associations and lacks control group

Question 14

What are cross sectional studies?

Answer 14

Observation of defined population at single point in time or time interval
Exposure and outcome determined at same time

Question 15

What are cross sectional studies used for and what are the disadvantages?

Answer 15

Investigating prevalence of disease and potential risk factors
Disadvantages - causality, confounding and recall bias

Question 16

What are case control studies?

Answer 16

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

Question 17

What are case control studies used for and what are the disadvantages?

Answer 17

Looking at potential causes of disease
Disadvantages - confounding, recall bias, selection of controls, time relationship

Question 18

What are Cohort studies?

Answer 18

Establish group of individuals in population (measures exposure)
Follow up over a period of time
Identify those that develop disease (outcome of interest)

Question 19

What are Cohort studies used for?

Answer 19

Estimating incidence of disease
Investigating causes of disease
Determining prognosis
Timing and direction of events

Question 20

What are the disadvantages of cohort studies?

Answer 20

Controls difficult to identify
Confounding
Blinding difficult
In rare diseases - need large samples
Expensive and time consuming

Question 21

What are RCTs?

Answer 21

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

Question 22

List 4 design elements of RCTs

Answer 22

Specification of participants - inclusion and exclusion criteria
Control groups
Randomisation
Blinding/masking - neither participants or researchers know who received which treatment

Question 23

List 2 inclusion or exclusion criteria

Answer 23

Age
Diagnosis or severity of disease

Question 24

Name an advantage of RCTs

Answer 24

Strongest evidence for causality

Question 25

What are the disadvantages of RCTs?

Answer 25

More difficult to design and conduct than observational studies
Still same risk for bias
Not suitable for all research questions

Question 26

What does PICO stand for?

Answer 26

Population
Intervention
Comparison
Outcome

Question 27

What are systematic reviews?

Answer 27

Literature review that uses systematic methods to collect secondary data, critically appraise research studies and synthesise studies

Question 28

What are the advantages of systematic reviews?

Answer 28

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

Question 29

What are the steps of a systematic review?

Answer 29

Well formulated question
Comprehensive data search
Unbiased selection
Assessment of papers
Synthesis of data

Question 30

How are statistically significant positive results often biased?

Answer 30

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

Question 31

What are meta-analyses?

Answer 31

Using statistical methods to combine the results of different studies

Question 32

What are the different data types in a meta-analysis?

Answer 32

Dichotomous - yes or no
Continuous - bp, weight

Question 33

What are the different types of heterogeneity?

Answer 33

Clinical - variation in participants, interventions, outcomes
Methodological - variation in methods used in studies
Statistical - variation in treatment effects above that expected by chance

Question 34

What is the Chi-squared test?

Answer 34

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)

Question 35

What is used to evaluate bodies of evidence?

Answer 35

GRADE
Grading of
Recommendations Assessment,
Development and
Evaluation

Question 36

What can lower the quality of a body of evidence?

Answer 36

High or unclear risk of bias
Inconsistency between studies - heterogeneity
Indirectness - studies not similar
Imprecision
Publication bias

Question 37

What is the CASP tool?

Answer 37

Critical appraisal skills programme
Checklists to help evaluate research studies