evidence based dentistry Flashcards
what is cross sectional study?
OBSERVATIONAL study that analyses data from…
- a population
- a representative subset
- a specific point in time
- recall biased group
- e.g a survey!
what is cohort study?
OBSERVATIONAL
- in which participants ar recruited for a study
- They are followed up over time
- Exposures and diseases are measured prospectively (likely, or expected to happen)
what is RCT - Randomnised Control trial / Clinical trial?
INTERVENTIONAL
- Participants allocated by chance to different interventions and followed up with outcomes assessed
- Key features
- Inclusion/Exclusion criteria
- Control/Comparison
- Blinding - reduces awareness and therefore bias
- Randomisation
- Disadvantages
- More difficult to conduct than OBSERVATIONAL
- Costly
- Ethical issues
- Not suitable for all types of research questions
what is case series report?
Description of medical history of one or more patients
Outcome of interest
Lacks control group
what is case control study?
People with a disease are matched to those without it
Earlier exposure to different factors are compared
lacks control group
Great for Aetiology
what is systematic review and meta analysis?
all the evidence for RCTs looking at effectiveness of a particular treatment are synthesised
- Require multiple RCTs in order to exist
- find literature > assess quality > combine it
what is prevalence and incidence?
Prevalence > Related to a specific point in time
Incidence > Is the rate something in a period of time
what is the risk?
- What are the chances
- Outcome - something that might happen
Calculating risk :-
risk = number of events of interest / total number of observations
- 24 people ski down a slope
- 6 fall
6/24
risk of falling = 0.25 -> 25%
what are odds?
odds = number of events of interest / number without the event
24 people ski down a slope
- 6 fall
6 fall/18 didnt fall = 0.33 odds of falling (usually not %)
risk reduction?
Be wary of risk reduction
- 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
what is absolute risk difference?
Difference between groups
- Risk of group 1 = 63%
- Risk of group 2 = 18%
- ARD = 63-18 = 45%
If no benefit then ARD = 0
risk = number of events of interest
—————————————
total number of observations
odds = number of events of interest
————————————-
number without the event
ARD = RISK 1 (%) - RISK 2 (%)
what is number needed to treat?
is the number of patients youd need to treat to prevent one from developing disease/condition/outcome
- Calculated as
NNT = 1/ARD
(ard is absolute risk difference)
- Therefore youd need to treat 3 people (cant have 2.22 people) to have a person experience pain relief of 50% in 4 hrs as scenario
criteria dictates
what is risk ratio?
RR = RISK 1 / RISK 2
e.g 63% and 18%
63/18 = 3.42
so person 3.42x more likely to get
pain relief than so
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
what is odds ratio?
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 %!
what is confidence intervals?
Taken a sample of participants/patients
- CI’s quantify level of uncertainity 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
