Evidence based dentistry

Question 1

What study design an observational study that analyses data collected from a population, or a representative subset, at a specific point in time

Answer 1

cross-sectional study

Question 2

What study design is a description of the medical history of one or more patients

Answer 2

case-series report

Question 3

What study design is when people with a disease are matched to those without it and earlier (or looking forward) exposure to different factors are compared

Answer 3

case-control study

Question 4

What study design is when partipants are recruited to a study and followed up over time. Exposures and diseases are measured prospectively

Answer 4

cohort study

Question 5

What study design is when participants are allocated by chance to different interventions and followed up and outcomes assessed

Answer 5

randomised controlled trial

Question 6

What study design is when all the evidence for RCTs looking at effectiveness

Answer 6

systematic review and meta analysis

Question 7

What study design is looking at e.g. amount of observation on linking to outcome

Answer 7

ecological study

Question 8

What study design is most appropriate for investigating whether nystatin prevents oral candidiasis in patients reciving treatment for head and neck cancer

Answer 8

RCT/ systematic review

Question 9

What study design is most appropriate to find out the incidence of oesophageal cancer in adults

Answer 9

cohort

Question 10

What study design is most appropriate to find out parents experiences of their child’s dental anaesthesia

Answer 10

cross sectional (snapshot in time)

Question 11

What study is most appropriate to find out whether teenagers with crossbites more likely to go on to develop TMJ disorders

Answer 11

case control (start with disorders and look back to see whether they crossbite -need less numbers)

cohort (but would need lots of people)

Question 12

What study is the most appropriate to find out the prevalence of cleft lip and palate in children born in the West coast of scotland

Answer 12

cross sectional study

cohort also possible

Question 13

What study is the most appropriate to find out what risk factors are associated with root resorption in patients who have undergone orthodontic treatment

Answer 13

case control

cohort also possible

Question 14

What does pico stand for

Answer 14

population
intervention
comparison group
outcome

Question 15

What are the 4 key features of an RCT

Answer 15

1. specification of participants (inclusion/exclusion)
2. control/comparison group
3. randomisation
4. blinding/masking

Question 16

what are ‘arms’ of a study

Answer 16

how many comparison groups you have

Question 17

what are a couple of ways you can randomise a study

Answer 17

by clusters e.g. schools
individually
stratified randomisation e.g randomise by different age groups to get a population representation

Question 18

why might it not always be possible to blind an experiment

Answer 18

• ethical reasons

- individual knows what group they are in based on the instructions they are given

Question 19

what people can you blind in an experiment

Answer 19

• participants
• clinicians (administrator of treatment)
• assessor of outcome
• data analyst

Question 20

How do you work out risk/ chance of something being true

Answer 20

numbers of “x” being true/ total

e.g. 6/24 when 24 is total

Question 21

How do you work out absolute risk difference

Answer 21

percentage risk/chance of intervention group - percentage risk/chance of control group

Question 22

how do you work out the risk ratio

Answer 22

intervention: control and divide through i.e. intervention/ control

intervention risk/chance = 80/100
control risk/chance = 75/100

80/75 = 1.07

Question 23

how do you work out the odds ratio

Answer 23

number of events of interest/number that didn’t experience event

e.g. 6/18 when total is 24

but express as a number not a fraction or ratio
divide through with the intervention on top

Question 24

The risk ratio [95% CI] for being very satisfied = 1.07 [0.92 to 1.24].
Is there sufficient evidence that the intervention is superior to the comparison

Answer 24

no (because 0.92 is below 1)

The CI needs to not overlap 1 to be sufficient evidence

Question 25

What information should you need to know about the design of a study before making decisions

Answer 25

- inclusion/exclusion criteria - side effects/ adverse outcomes - does it clinically benefit patients - how were they randomised - were they blinded - who has funded the trial

Question 26

Describe the difference between starting and modified risk reductions. how does this help determine between relative and absolute risk reductions.

Answer 26

In drug studies the starting and modified risks are the chances of the outcome in the untreated and treated groups (those who did not take the drug and those that did) e.g. control group = 6/123 = 4.9% intervention = 1/123 = 0.8% 4.9% down to 0.8% = 84% reduction so could argue that Dental treatment could cut the risk of babies being born early by 84% when actually it hasn't made that much of a difference 84% reduction is the RELATIVE RISK REDUCTION 4.1% reduction is the ABSOLUTE RISK REDUCTION

Question 27

What is the number needed to treat (NMT) how do you work it out

Answer 27

The number of patients you would need to treat to prevent one patient from developing the disease/ condition/ outcome Numerically: 1/ Absolute Risk Difference NNT for paracetamol = 1/ 0.45 = 2.22 Would need to treat 3 people with paracetamol post-operatively to have one person experience pain relief of >50% in 4 hours

Question 28

In a risk ratio what is the value of no difference

Answer 28

1

Question 29

In an odds ratio what is the value of no difference

Answer 29

1

Question 30

How 'solid' is the evidence from different studies in order

Answer 30

``` most solid - systematic reviews and meta analysis - randomised controlled trials (RCTs) - cohort studies - case control studies - cross sectional surveys - ecological studies - case series and case reports - ideas, editorials and opinions least solid ```

Question 31

Advantages of RCTs | Disadvantages of RCTs

Answer 31

- Provide strongest and most direct epidemiologic evidence for causality - Non-blinded RCTs may overestimate treatment effects eg estimates of effect from trials with inadequately concealed allocation have been 40% larger than clinical trials with adequately concealed random allocation - More difficult to design and conduct than observational studies - Still some risk of bias and generalisibility often limited - Not suitable for all research questions

Question 32

what are case report/ case series used for and what are their disadvantages

Answer 32

used for: Identify new disease outcome Hypothesis generation disadvantages Cannot demonstrate valid statistical associations Lack of control group

Question 33

What are cross-sectional studies used for and what are their disadvantages

Answer 33

used for: - Estimating prevalence of a disease - Investigate potential risk factors Disadvantages - Causality - Confounding - Recall bias

Question 34

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

Answer 34

Used for: Looking at potential causes of disease ``` Disadvantages: Confounding Recall / selection bias Selection of controls Time relationships (did exposure occur before disease? if it didn't it can't have caused it) ```

Question 35

What are cohort studies used for and what are their disadvantages

Answer 35

Used for: - Estimating incidence of disease - Investigating causes of disease - Determining prognosis - Timing and direction of events Disadvantages - Controls difficult to identify - Confounding - Blinding difficult - For rare diseases- need large samples - Very expensive/ time consuming