Statistics & Landmark Trials Flashcards
Define Absolute Risk
The number of events in a group, divided by the number of people in that group.
What is the absolute risk control (ARC)
Absolute risk in the control group (i.e. number of events in control arm divided by total numbers in control arm)
What is the absolute risk treatment (ART)
Absolute risk in the treatment group (i.e. number of events in treatment arm divided by total numbers in treatment arm)
Absolute risk reduction
ARC - ART
Number needed to treat
1 / Absolute risk reduction
Relative Risk
ART / ARC
Relative Risk Reduction
(ARC - ART) / ARC or 1 - RR
Sensitivity
TP / (TP + FN)
Ability for a test to descriminate if a person has a condition
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Specificity
TN / (TN + FP)
Ability for a test to discrimiate if a person doesn’t have a condition
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Positive Predictive Value
TP / (TP + FP)
Describes the performance of a test. I.e. the likelihood that a positive result is accurate.
Negative Predictive Value
TN / (TN + FN)
Describes the performance of a test. I.e. the likelihood that a negative result is accurate.
What is Prevalence?
The proportion of a population found to have a condition. e.g. 1 in 10,000.
What is Incidence?
A measure of the probability of occurrence of a given medical condition in a population within a specified period of time. E.g. 1 in 10,000 per year. It can be thought of as the rate as which a disease proliferates in the population.
Odds Ratio
Odds of the event : non-event
OR = 1 is no difference
What are the main problems associated with meta-analysis?
- Publication bias
- Language bias
- Replication bias
- Requires some homogeneity between studies
What is type 1 error
- A.K.A. Alpha error.
- Incorrect rejection of the null hypothesis
- I.e. finds a difference where non-exists
What is a type 2 error?
- Incorrect acceptance of the null hypothesis
- i.e. saying there is no difference when there really is
What are observational studies?
- The investigator does not assign exposures
- There can however be comparison groups
- With comparison groups => Analytical Study
- Cohort study
- Case-control study
- Cross sectional study
- Without comparison groups => Descriptive Study
- Case report
- Case series
What is the heirarchy of medical evidence?
- 1a) Systematic review of RCTs
- 1b) Individual well designed RCT
- 1c) All or none study
- 2a) Systematic review of Cohort studies
- 2b) Individual cohort study
- 3a) Systematic review of case-control studies
- 3b) Individual case-control study
- 4) Case-series
- 5) Expert opinion, bench research, first principles
What is the grading of recommendation for scientific literature?
- A - Consistent level 1 studies
- B - Consistent level 2 or 3 studies, or extrapolations from level 1
- C - Level 4 studies, or extrapolations from level 2 or 3
- D - Level 5 evidence, or troubling/inconsistent studies at any level
Describe the process required for drug approval
- Pre-clinical studies
- Phase 0
- First in human
- Micro dosing
- Preliminary data on pharmacokinetics
- Phase 1
- Healhty volunteers
- Dose-ranging
- Phase 2
- Larger groups
- Efficacy testing
-
Phase 3 => at least 2 required to market
- RCTs to assess efficacy
- Phase 4
- Post marketing surveillance
What was the OPTIMISE (2014) trial investigating?
In high-risk patients undergoing gastrointestinal surgery, does a cardiac output-guided haemodynamic therapy algorithm compared to clinician-guided standard therapy reduce death and major morbidity within 30 days?
What was the intervention protocol in OPTIMISE?
- Colloid and dopexamine administration from induction of anaesthesia to 6 hours after end of surgery guided by LiDCO monitor.
- 250ml bolus colloid over 5 minutes – positive response if rise in stroke volume of at least 10% sustained for 20 minutes.
What was the outcome from OPTIMISE?
There was a reduction in 30 day composite adverse major outcomes, but not statistically significant (p = 0.07). No difference in other end points
What factors affect the positive predictive value?
Sensitivity, Specificity and Prevalence.
What is the Positive likelihood ratio?
Sensitivity / False Positive Rate
What is the negative likelihood ratio?
False negative rate / Specificity