critical appraisal 2 Flashcards
For research questions about effectiveness of one treatment compared to another what study design is the best to use?
For research questions about effectiveness of one treatment compared to another RCTs are considered the gold standard study design (primary).
What is CASP?
The Critical Appraisal Skills Programme (CASP) helped to develop an evidence-based approach in health and social care, working with local, national and international groups. CASP aims to help individuals develop skills to find and make sense of research evidence, helping them to apply evidence in practice.
What framework do you have to look at when deciding if the trial has a clearly focussed issue?
PICO.
What is a RCT?
Sometimes referred to as a Clinical Trial
RCTs considered the gold standard study design
For effectiveness and efficacy
Particularly useful for clinical studies
Provides strongest evidence on effectiveness of treatments.
What questions should you ask yourself when deciding if the results of a trial are valid?
Was the assignment of treatments to patients randomized?
Were all of the patients who entered the trail accounted for at its conclusion?
Were patients, health workers and study personnel “blind” to treatment?
Were the groups similar at the start of the trial?
Aside from the experimental intervention, were the groups treated equally?
*There are a few case examples on these slides.
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What is the absolute risk difference?
Difference in risk between groups
“Risk” or “chance” of at least 50% pain relief in 4 hours
“good” outcome measure
Risk in paracetamol group= 40/63= 63%
Risk in placebo group=5/27= 18%
Risk Difference = 63% - 18% = 45%
45% more patients experienced pain relief in the paracetamol group
With all estimates we calculate a CONFIDENCE INTERVAL around it- this is the range that the ARD will take in the population (95 times out of 100 the CI will contain the TRUE ARD).
What is a confidence interval?
The range of values the ARD will take in the population
95 times out of 100 the CI will contain the TRUE population ARD
What value would ARD take if there was no benefit of paracetamol over placebo? 0 (value of no difference) So 95% CI should not overlap “0” ARD= 45% 95% CI= [30% to 55%] “Sufficient evidence”.
What is the NNT?
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
NNT for statins ~ 33.
What are some advantages and disadvantages of the split mouth technique?
Possible advantages of split-mouth trials over parallel group;
Each participant acts as own control-reduces inter-individual variation
Therefore, fewer participants are required to obtain same study power as parallel group
Every participant receives each intervention, therefore good for determining preferences
Possible disadvantages
Carry-across effects (“leakage”)
Selection of patients (need to have matching carious teeth) might limit external validity
Statistical analysis more sophisticated, and is usually not done!
What does IIT mean?
Intention to treat (ITT)
Analyse the data as though the switchers were still in the NEW agent group
More conservative (PREFERRED)
Pragmatic- in real life this will happen
Drop outs
Can impute data
(LOCF/ BOCF).
What does “per protocol” mean when someone has dropped out of a trial?
Per Protocol
Analyse the data according to the treatment actually received
Efficacy to explain the effects of the intervention itself.
