evidence based dentistry p162

Question 1

PICO

Answer 1

Participants - who is the review interested in studying
Intervention (Exposure) - what is the intervention(s) of interest
Comparison - what will the interventions be compared to
Outcome - which outcomes will tell you which intervention is most effective

Question 2

what is CASP

Answer 2

Critical Appraisal Skills Programme

for RCTs and separate checklist of systematic review and meta analysis

Question 3

section A in CASP

Answer 3

Are the results of the study valid?

1. Did the review ask a clearly focused question
2. Did the authors look for the right type of papers
3. Did you think all the important relevant studies were included
4. Did the review’s authors do enough to assess quality of the included studies
5. If the results of the review have been combined was it reasonable to do so

Question 4

Section B in CASP

Answer 4

What are the results?

6. What are the results of the review
7. How precise are the results

Question 5

Section C in CASP

Answer 5

Will the results help locally?

8. Can the results be applied to the local population
9. Were all the important outcomes considered
10. Are the benefits worth the harms and costs

Question 6

prevalence

Answer 6

related to a specific point in time

Question 7

incidence

Answer 7

is the rate something in a period of time

Question 8

risk

Answer 8

what are the chances

outcome - something that might happen

Question 9

risk =

Answer 9

number of events of interest / total number of observations

e.g. 24 people ski down a slope, 6 fall
6/24
risk of falling = 0.25 -> 25%

Question 10

odds =

Answer 10

number of events of interest / number without the event

e.g. 24 people ski down a slope, 6 fall
6 fall/18 didnt fall = 0.33 odds of falling (usually not %)

Question 11

why be wary of risk reduction

Answer 11

e.g new drug reduces prevalence of disease from 4.9% to 0.8%

Small difference

but as a risk reduction that is 84% reduction (false view given)

RELATIVE RISKS THAT SEEM LARGE MIGHT NOT MEAN MUCH IF STARTING RISK IS SMALL

Question 12

absolute risk difference

Answer 12

Difference between groups
- Risk of group 1 = 63%
- Risk of group 2 = 18%
- ARD = 63-18 = 45%
If no benefit then ARD = 0

ARD = RISK 1 (%) - RISK 2 (%)

Question 13

number needed to treat

Answer 13

is the number of patients youd need to treat to prevent one from developing disease/condition/outcome

NNT = 1/ARD

Question 14

risk ratio

Answer 14

risk 1 / risk 2

e.g 63% and 18%
63/18 = 3.42
so person 3.42x more likely to get pain relief than someone in the placebo group

Can’t get 0 value for this, so if the answer comes to 1 then there is no difference in risk ratio between the two criteria

Question 15

relevant risk reduction

Answer 15

RRR = RISK1 - RISK2 / RISK 1

e.g 63% and 18%
63-18/63
45/63
= 71% risk reduction

Question 16

odds ratio

Answer 16

Ratio of odds of pain relief in the both groups (usually intervention/control studies)

Work out odds for each group, Then divide odds over one another

OR = ODDS 1/ ODDS 2
e.g
O1 -> 40/23 = 1.74
O2 -> 5/22 = 0.23

1.74/0.23 = 7.56
*Remember odds not in %!

Question 17

confidence intervals

Answer 17

quantify level of uncertainty of risk ratios etc

For a ratio where value of no difference is 1

• If the confidence interval (contains/overlaps/straddles 1)
  
  • Insufficient evidence = that there is a difference between e.g paracetomol and placebo
• if this interval does not (contain/overlaps/straddles 1)
  
  • Sufficient evidence to say there is a difference
  • i.e if value > 1

Question 18

CI straddles 1

Answer 18

Insufficient evidence = that there is a difference between e.g paracetomol and placebo

Question 19

CI doesn’t straddle 1

Answer 19

Sufficient evidence to say there is a difference
• i.e if value > 1

Question 20

systemic review process

Answer 20

1. Well formulated question
Using PICO

• How effective is paracetamol (I) for pain relief (O) compared to placebo (C ) after surgical removal of lower wisdom teeth in adults (P)?

2. Comprehensive data search
• Medline
• Reference lists
• Hand Searching
• Multiple languages
• being aware of reporting bias
➡ Publication bias
➡ Time lag bias
➡ Language bias
➡ Citation bias

3. Unbiased selection and abstraction process
• Selection of relevant papers
• Data extraction to a predefined data extraction form
• Process should be conducted independently by >2 reviewers
• Clear reasons described for why papers were excluded

4. Assessment of papers
• Look at methodology
➡ How well the studies have been designed and conducted
• Process should be conducted by at least >2 reviewers
• Results of the reflection should be used in the analysis

5. Synthesis of data
• Pooling process
‣ Qualitative - narrative
‣ Quantitive - meta-analysis
➡ Using statistical methods to combine the results of different studies
➡ Integrate findings
➡ Pool data
➡ Identify overall trend

Question 21

tools for assessing quality of papers

Answer 21

comoposite scales

component approach

Question 22

adv of metal analysis

Answer 22

Increase in power

More precise

ability to answer questions not posed by individual studies

Question 23

disadv of meta analysis

Answer 23

Can be misleading

Should only be done when
✓Minimal differences across studies
✓Same outcome measure
✓Data in each study are available

Question 24

discontinuous (biniary) data

Answer 24

e.g illness or not/death or not/ birth or not

Odds ratio (OR)

Risk ratio (RR)

Percent risk reduction, or relative risk reduction (RRR)

Risk difference, or absolute risk reduction (RD)

Number needed to treat (NNT) (1/RD)

Question 25

continous data

Answer 25

e.g Blood pressure, weight, amount of pain Weighted mean difference * can only be used when all the outcomes are using the same scale Standardised mean difference * For when all the studies are assessing the exact same outcome but do it in a variety of ways e. g example of depressed patients but using varied psychometric scales to calculate it

Question 26

forest plot

Answer 26

Vertical line divides the graph - called the line of no effect LHS - New treatment that has been more beneficial RHS - No Tx or that a standard Tx has been more beneficial the further to the left or further to the right it was, the more pronounced the benefit was found to be If results close to or on the line = no effect Boxes - size of study - bigger the box the bigger the study Line through box - confidence interval * narrower the line the narrower the confidence interval * the wider the line = less certain If the CI line touches the line of no effect when crossing the box then it means = no statistical signficance ``` Diamond = combined studies height = combined study size width = combined confidence interval ```

Question 27

clincal heterogenity

Answer 27

- Variation in participants - Interventions - Outcomes - Study design

Question 28

metholodigical heterogeneity

Answer 28

Variation in methods used in studies e.g quality of allocation concealment

Question 29

statistical heterogeneity

Answer 29

Excessive variation in the results of studies - Variation in treatment effects above that expected by chance \*Statistical heterogeneity = poor overlap of confidence intervals - i.e outliers whose horiztontal lines don’t overlap others vertically If P\<0.1 then stats are too heterogenous so should probably not pool together

Question 30

sub group analyses when

Answer 30

Where it is expected in advance that certain features may alter the effects of an intervention e.g Gender, age groups, specific disease subtypes

Question 31

evaluating results of meta analysis (Cochrane)

Answer 31

G - grading of R - Recommendations A - Assessment D - Development and E - Evaluation

Question 32

factors that lower quality in a study (5)

Answer 32

High or unclear risk of bias * Due to design issues or poor conduct of studies Inconsistency between studies * Heterogeneity Indirectness * PICO- were all studies similar? Imprecision * Numbers and CIs Publication bias * Likely that negative/null results not published?

Question 33

summary of findings table

Answer 33

Summary of the key findings from a systematic review It presents * Quality of the evidence * Magnitude of the effect * Reasons behind judgements Format 1. PICO 2. Outcomes 3. Results - No. studies and participants - Relative and Absolute effects - Certainty and quality of evidence - Notes