Review Note
Last Update: 02/18/2024 05:30 AM
Current Deck: Part 2::2. Clinical oncology::Non-clinical topics
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ClinOnc | Evidence based medicine
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- Definition: Conscientious and judicious use of current best evidence in making decisions about individual patient care
- Steps: 5 steps in incorporating best about individual patient care
- Formulate clear and focused question specifying (PICO)
- Patinet population
- Intervention/exposure
- Comparator/control
- Clinical outcome of interest
- Search for evidence: Cochrane, Medline, PubMed, CINAHL, other: colleagues, experts, textbooks
- Evaluate / appraise validity of evidence (including internal and external validity)
- Validity checklists, e.g. CONSORT, JAMA
- Apply research information to patient care
- Evaluate effectiveness through planned review
- Advantages
- Best practice treatment
- Knowledge updated for clinician
- Identifies areas requiring further research
- Develop skills of critical evaluation of evidence
- Disadvantages
- Time consuming
- May be difficult to access publications
- Validity of trial methods and potential for bias
- May not be applicable ot specific patient or generalisable
- Often conflicting or no evidence
- Levels of evidence: Aim - rank according to degree to which bias has been eliminated from study design.
- NHMRC levels of evidence (for evaluation of an intervention):
- Level I: Evidence obtained from systematic review fo all RCTs
- Level II: Evidence obtained from one well-designed RCT
- Level III: Evidence obtained from non-randomised trials, case-control or cohort studies
- III-1: A pseudo-randomised controlled trial (i.e. alternate allocation or some other method)
- III-2: A comparative study with concurrent controls
- Non-randomised experimental trial
- Cohort study
- Case-control study
- Interrupted time series with a control group
- III-3: A comparative study without concurrent controls
- Historical control study
- Two or more single arm studies
- Interrupted time seres wihtout a parallel control group
- Level IV: Case series with either post-test or pre-test/post-test outcomes
- Notes on levels of evidence
- Several different bodies have proposed categorisations for levels of evidence, and they are not all the same (e.g. a single well-conducted RCT with narrow confidence intervals is considered level I evidence in some schemas, but not by NHMRC)
- The categorisation of levels of evidence is different for different quesitons. Above is for assessing an intervention. However, different schemas are used for assessing diagnostic accuracy, prognosis, aetiology and screening interventions respectively.
- Strength of recommendations: leads to levels of recommnedation:
- A: level 1
- B: Level 2 or 3 or extrapolation from level 1
- C: Level 4 or extrapolation from level 2 or 3
- D: Expert opinion or very inconsistent evidence
- Benefits
- Classifies evidence
- Draws attention to obtain highest level of evidence on which to base decisions
- Limitations: Level does not guarantee quality of individual evidence, does not determine applicability to specific patient
- Assessing validity
- Internal validity
- Bias
- Blinding of subjects
- Blinding of other relevant individuals (clinicians, data colectors, outcome adjudicators, data analysists)
- Loss to follow up (missing outcome data)
- Failure to adhere to assigned intervention
- Stopping early for benefit
- Publication bias
- Chance
- Random error
- Minimised by studying a large number of patients
- p-values describe the probability that if the null hypothesiswere true, the study would find a difference as large, or larger, than the one found
- External validity
- Whether the results of the study apply to patients outside of the study, particularly the specific patient (or population) being considered by the EBM practitioner
- Depends on:
- Study eligibility criteria
- Demographics of patients actually enrolled
- Meta-analysis
- Useful when evidence is conflicting ro individual trials do not yield statistically significant result due to inadequate power
- E.g. Oxford overview of chemotherapy, endocrine therapy and RT in breast, chemo in H&N SCC, chemo in neoadjuvant oesophagus
- Only as good as the trials it includes, need to include unpublished and only good quality, e.g. Cuzick MA in PMRT
- Possible for one large RCT to overpower remainder
- RCTs
- Aim: eliminate systematic differences (known and unknown) between treatmetn groups other than the intervention under investigation
- Blinding eliminates treatmetn bias, reporting bias and assessment bias
- Quality of RCT based o nrandomisation process, balance between groups, ITT anlaysis, length of FU, significance of results
- Only useful in extent to which can be applied to individual patient, e.g. INT 0099 AL Sarraf trial in NPC did not include Asian
- Case control and cohort studies
- Role in rare disease and investigating aetiology, e.g. in utero DES exposure link to clear cell ca of cervix/vagina
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