Evidenced-based Dentistry

Question 1

What are the advantages of a sytematic review compared to a single study

Answer 1

• Saves readers time
• Provides reliable evidence
• Resolves inconsistencies – single studies brings all these conflicting studies together
• Identifies gaps
• Identifies where questions have been fully answered and it is unethical to conduct anymore studies
• Explores differences between studies – identifying factors that influence the effect of an intervention

Question 2

What is the importance of systematic reviews

Answer 2

• Reduce large quantities of info into manageable portions, makes it easy for professionals to access research
• Formulate policy and develop guidelines - guidelines are based on these
• Efficient use of recourses – studies have already been done
• Increased power and precision - small studies alone don’t mean much but pulled together, it gives greater power in estimates
• Limit bias and improve accuracy

Question 3

What is a process of systematic review

Answer 3

• Authors – two or more authors, one is a topic expert and the other methodological
• Study protocol – in advance set out what they plan to do methodologically
• Create a specific question using PICO
• Search strategy
  o Using multiple electronic databases
  o Include published and unpublished literature
  o Ensure search is both comprehensive and repeatable
• Inclusion/exclusion
  o Specific
  o Agreed in advance
• Critical appraisal
  o Thorough
  o Assess for risk of bias
• Synthesis
  o Can be qualitative (narrative) or quantitative (meta-analysis)

Question 4

What are the key characteristics of a systematic review

Answer 4

o well formulated question
o comprehensive data search
o unbiased selection and abstraction process
o assessment of papers
o synthesis of data

Question 5

How do we produce a well formulated question

Answer 5

• Use PICO

Question 6

PICO

What is meant by participants

Answer 6

who is the review looking at

Question 7

What is meant by interventions

PICO

Answer 7

What is the px being exposed to

Question 8

What is the comparison

PICO

Answer 8

• control group
• what will the intervention be compared to

Question 9

What is outcome

PICO

Answer 9

which outcome will tell you which intervention is most effective

Question 10

What do we define the inclusion/exclusion criteria based on

Answer 10

the question
PICO

Question 11

What should we consider using when doing the comprehensive data search

Answer 11

o Electronic Databases
o Reference lists
o Hand searching
o English language/non-english language
speak to librarians for help

Question 12

What are the different reporting bias

Answer 12

positive results are more likely to be
o Published – publication bias
o Published rapidly – time lag bias
o Published in English – language bias
o Cited by others – citation bias

Question 13

How do we conduct an unbiased selection and abstraction process

Answer 13

• Select relevant papers
• Data extraction to a predefined data extraction form
• Process should be conducted independently by at least 2 reviewers
• Clear description of reasons for exclusion
• Adequate description of included studies
• Details of studies funding source

Question 14

How do we assess the papers

Answer 14

• How well the studies have been designed and conducted – methodology
• Process should be conducted independently by at least 2 reviewers
• Results of the assessment should be reflected in the analysis

Question 15

What can the assessment of papers be used as

Answer 15

o as a threshold for inclusion of studies
o as a possible explanation for differences in results between trials
o in sensitivity analyses
o as weights in statistical analysis of results

Question 16

What are the 2 main quality assessment tools in the assesment of papers

Answer 16

composite scales
component approach

Question 17

What is composite scales

Answer 17

assign numerical value to individual items to provide overall estimate of quality

Question 18

What is a component approach

Answer 18

assess relevant methodological aspects individually e.g randomisation, blinding, dropouts

Question 19

Why is the component approach preferred to the composite scale

Answer 19

more specific in the downfalls of the studies
don’t know the specifics of what made the study unreliable in the composite scale

Question 20

What does the risk of bias assessment consist of

done as part of the assessment of papers

Answer 20

o determines extent to which results of study can be believed
o direction of bias: causes overestimation or underestimation of effect
o magnitude of bias

Question 21

What aspects of methodology does a risk of bias assessment for RCT consist of

Answer 21

Random sequence generation (selection bias)
Allocation concealment (selection bias)
Blinding (outcome assessors)
Incomplete outcome data (attrition bias)
Selective outcome reporting (reporting bias)
Other bias

Question 22

What is a variation in risk of bias be an explanation for

Answer 22

heterogeity between results of different studies
significant risk of bias in included studies should give rise to cautious conclusions in a systematic review

Question 23

What are the two types of data synthesis

Answer 23

qualitative - narrative
quantitative - metanylsis

Question 24

When is meta-analysis inappropriate

Answer 24

when not enough data or heterogeneity exists

Question 25

What is meta-analysis

Answer 25

• This is the process of using statistical methods to combine the results of different studies

Question 26

What are the aims of meta-analysis

Answer 26

• Aim is to integrate findings, pool the data and identify overall trends in results
  o Calculates a treatment effect based on pooled data from a group of studies
  o Estimates a common tx effect across studies
  o Improves precision of a point estimate by using all available data

Question 27

What are the advantages of meta-analysis

Answer 27

o increase in power
o improvement in precision
o ability to answer questions not posed by individual studies

Question 28

What are the disadvantages of meta-analysis

Answer 28

potential to mislead, need to be careful when it is undertaken

Question 29

When should meta-analysis be undertaken

Answer 29

o minimal differences in characteristics across studies
o same outcome measure
o data in each study is available

Question 30

What are the 2 different types of data

Answer 30

dichotomous
continous

Question 31

What is dichotomous data

Answer 31

1 out of 2 forms
e.g death or no death

Question 32

What are the choices of summary statistics for dichomotous data

Answer 32

• odds ratio
• risk ratio
• percent risk reduction or relative risk reduction
• risk difference or absolute risk reduction
• number needed to treat

Question 33

What are the summary statistic choices for continous

Answer 33

• weighted mean difference
• standardised mean difference

Question 34

When is more weight given to a study

Answer 34

o more participants
o more events
o lower variance

Question 35

How can results be displayed graphically

Answer 35

forest plot

Question 36

Describe the different features of a forest plot

Answer 36

• Horizontal line at bottom is the scale measuring tx effect
• Vertical line in the middle si where tx and control have same effect and there is no different between the two
• For each study there is an ID, data is then divided into the experimental and control group, a weight is given
• There is then a label above the graph to tell you what ratio has been used and the data is shown using a line and also numerically
• Each study has a blob which is placed where the data measure the effect
• The horizontal line running through the blob is called a confidence interval and is a measure of how we think this result may vary with chance
• The wider the line is, the less confident and if it overlaps the vertical no effect line, then insufficient evidence to support a difference in the two interventions

Question 37

What are the 3 types of heterogeneity

Answer 37

• clinical
• methodological
• statistical

Question 38

What is clinical heterogenity

Answer 38

the way study has been conducted
variation in participants, interventions, outcomes, study design
e.g age, baseline disease severity, dosage etc

Question 39

What is methodological heterogeneity

Answer 39

Variation in methods used
* Variations in study design and risk of bias
* e.g use of allocation concealment

Question 40

What is statistical heterogeneity

Answer 40

Excessive variation in results of studies

Variation in the intervention effects being evaluated in the different studies and is a consequence of clinical or methodological diversity

Manifests itself in the observed intervention effects being more different from each other than one would expect due to chance alone

Question 41

How do we identify heterogeneity

Answer 41

o if studies are estimating the same thing, we would expect confidence intervals to overlap to a large extent
o statistical heterogeneity may appear in a forst plot as poor overlap of confidence intervals
o Chi squared test
o P<0.1 demonstrates statically significant heterogeneity and then it may be inappropriate to pool data
o I2 statistic is the percentage variation due to heterogeneity rather than chance and <50% is acceptable

Question 42

What is subgroup analysis

Answer 42

• Studies divided into sub groups
• Should be decided in advance, not after seeing data
• Done where it is suspected in advance that certain features may alter the effect of an intervention

Question 43

What is the main aim of subgroup analysis

Answer 43

• The main aim of a subgroup analysis is to identify either consistency of or large differences in the magnitude of treatment effect among different categories of patients.

Question 44

What are examples of subgroups that could be utilised in subgroup analysis

Answer 44

o gender
o age groups
o specific disease subtypes

Question 45

What is sensitivity analysis

Answer 45

Repeating metaanalysis
.g if some studies eligibility is dubious due to a lack of full details: run the metaanalysis the first time using the dubious studies and the second time using the non-dubious studies
* Need for sensitivity analysis usually decided in review process but can be predecided in the protocol

Question 46

What info can the sensitivity analysis give us

Answer 46

• When sensitivity analyses shows that the overall result and conclusions are not affected by the ‘dubiosness’ then the results can be regarded wit a higher degree of sensitivity
• On the other hand, it may show that the missing information from these dubious studies has a large impact on results and so the search for the missing info can be undergone e.g contacting trial authors

Question 47

What is the fixed effect

Answer 47

o Assumes studies are so similar that they are effectively different parts of one large study
o Assumes that the true answer for each study is the same
o If I2 <50% (heterogeneous) then can use this model of meta-analysis

Question 48

What is the random effect

Answer 48

o Assumes studies are slightly different
o Assumes that the true answer for each study will be slightly different
o More conservative/wider CI
o If I2 >50% then can use this model of meta-analysis

Question 49

What is GRADE

Answer 49

• Used to estimate certainty of evidence
  o high
  o moderate
  o low
  o very low

Question 50

What are the 5 factors that can lower the quality grade

Answer 50

o high or unclear risk of bias – due to design issues or poor conduct of studies
o inconsistency between studies – heterogeneity
o indirectness – pico
o imprecision – numbers and CI
o publication bias – likely that negative/null results not published