Evidence based dentistry Flashcards
What study design an observational study that analyses data collected from a population, or a representative subset, at a specific point in time
cross-sectional study
What study design is a description of the medical history of one or more patients
case-series report
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
case-control study
What study design is when partipants are recruited to a study and followed up over time. Exposures and diseases are measured prospectively
cohort study
What study design is when participants are allocated by chance to different interventions and followed up and outcomes assessed
randomised controlled trial
What study design is when all the evidence for RCTs looking at effectiveness
systematic review and meta analysis
What study design is looking at e.g. amount of observation on linking to outcome
ecological study
What study design is most appropriate for investigating whether nystatin prevents oral candidiasis in patients reciving treatment for head and neck cancer
RCT/ systematic review
What study design is most appropriate to find out the incidence of oesophageal cancer in adults
cohort
What study design is most appropriate to find out parents experiences of their child’s dental anaesthesia
cross sectional (snapshot in time)
What study is most appropriate to find out whether teenagers with crossbites more likely to go on to develop TMJ disorders
case control (start with disorders and look back to see whether they crossbite -need less numbers)
cohort (but would need lots of people)
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
cross sectional study
cohort also possible
What study is the most appropriate to find out what risk factors are associated with root resorption in patients who have undergone orthodontic treatment
case control
cohort also possible
What does pico stand for
population
intervention
comparison group
outcome
What are the 4 key features of an RCT
- specification of participants (inclusion/exclusion)
- control/comparison group
- randomisation
- blinding/masking
what are ‘arms’ of a study
how many comparison groups you have
what are a couple of ways you can randomise a study
by clusters e.g. schools
individually
stratified randomisation e.g randomise by different age groups to get a population representation
why might it not always be possible to blind an experiment
- ethical reasons
- individual knows what group they are in based on the instructions they are given
what people can you blind in an experiment
- participants
- clinicians (administrator of treatment)
- assessor of outcome
- data analyst
How do you work out risk/ chance of something being true
numbers of “x” being true/ total
e.g. 6/24 when 24 is total
How do you work out absolute risk difference
percentage risk/chance of intervention group - percentage risk/chance of control group
how do you work out the risk ratio
intervention: control and divide through i.e. intervention/ control
intervention risk/chance = 80/100
control risk/chance = 75/100
80/75 = 1.07
how do you work out the odds ratio
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
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
no (because 0.92 is below 1)
The CI needs to not overlap 1 to be sufficient evidence
What information should you need to know about the design of a study before making decisions
- inclusion/exclusion criteria
- side effects/ adverse outcomes
- does it clinically benefit patients
- how were they randomised
- were they blinded
- who has funded the trial
Describe the difference between starting and modified risk reductions.
how does this help determine between relative and absolute risk reductions.
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
What is the number needed to treat (NMT)
how do you work it out
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
In a risk ratio what is the value of no difference
1
In an odds ratio what is the value of no difference
1
How ‘solid’ is the evidence from different studies in order
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
Advantages of RCTs
Disadvantages of RCTs
- 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
what are case report/ case series used for and what are their disadvantages
used for:
Identify new disease outcome
Hypothesis generation
disadvantages
Cannot demonstrate valid statistical associations
Lack of control group
What are cross-sectional studies used for and what are their disadvantages
used for:
- Estimating prevalence of a disease
- Investigate potential risk factors
Disadvantages
- Causality
- Confounding
- Recall bias
What are case control studies used for and what are the disadvantages
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)
What are cohort studies used for and what are their disadvantages
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
