Lecture 7 Flashcards
What is a statement of risk?
A statement about the dangers of something that can either be believed or disbelieved.
What are important factors to be included in a risk/benefit experiment?
- Realistic time scale
- Statistically valid (clear outcome)
- Multiple tests and repeats
- A control group (while considering fairness)
- Minimal side effects
- Ethical
- Unbiased
- Representative
Define relative risk (RR)
The increase in incidence of a disease in the exposed group compared to the non-exposed group, found by calculating ratio of the probabilities of an event occurring in the exposed group to that in the non-exposed group.
What is the equation for relative risk?
RR = relative risk
p = probability
What is the equation for absolute risk increase?
ARI = absolute risk increase
p = probability
What is the equation for relative risk increase (RRI)?
RRI = relative risk increase
p = probability
What is the equation for the number needed to harm (NNH)?
NNH = number needed to harm
ARI = absolute risk increase
What are relative risk increase and number needed to harm measured in?
%
Define relative risk of success (RR)
The ratio of the probabilities of a positive outcome in the treated group (i.e. reduced incidence) to that in the non-exposed group.
What is the equation for the relative risk of success?
RR = relative risk
p = probability
What is the equation for absolute risk reduction?
ARR = absolute risk reduction
p = probability
What is the equation for relative risk reduction?
RRR = relative risk reduction
p = probability
What is the equation for the number needed to treat?
NNT = number needed to treat
ARR = absolute risk reduction
What method can be used to determine if a trial result is significant?
The null hypothesis can be tested against.
What is the p-value of significance if we want to be 95% confident that a result is not due to chance?
p = 0.05 (a.k.a 5% probability that the result is due to chance)
Define null hypothesis
The hypothesis that there is no change in the outcome of a trial for a treated group compared to a control group.
Define standard error
A measure of the statistical accuracy of an estimate.
For a graph (bar chart) of the recovery rate of a control group and a treated group, how can the significance of the treatment be determined?
The treatment is significant if error bars do not overlap.
Define standard deviation
The square root of the variance.
What is the equation for standard deviation?
s = standard deviation
N = number of measurements made
x = measurement
x̄ = mean measurement
What is the equation for the standard error of the mean (SEM)?
SEM = standard error of the mean
s = standard deviation
N = number of measurements made
What is the student’s t-test?
A useful measurement when comparing small samples of two distinct groups (test and control) to look for a significant difference.
The student’s t-test is an _________ test when the two populations don’t depend on one another.
Unpaired
What is a single-tailed test?
A test that is only concerned with the significance of one end of the data (so either greater than or less than a specific value).
How is the student’s t-test carried out?
The ratio of the difference in mean values to the standard error of the difference is taken.
What is the equation for the student t-test?
t = statistic value
x̄ = mean measurement
SE = standard error of the difference in the means
s = standard deviation
N = number of measurements made
What is the equation for the degrees of freedom for an unpaired t-test?
DF = degrees of freedom
N = number of measurements made
What is a paired t-test?
A t-test that is taken for a single sample (so measurements are taken before and after treatment). This means that each measurement is paired.
What is the equation for the degrees of freedom of a paired student t-test?
DF = sample size - 1
What is a chi-squared test?
A test used to determine the significance of the difference between a set of measured (observed) values and the matching expected values.
What is the equation for the chi-squared test?
χ² = statistic value
O = observed value
E = expected value
What is the equation for the degrees of freedom for the chi-squared test?
DF = degrees of freedom
N = sample size
Define Quality-Adjusted Life Years (QALY)
An attempt to measure the benefit of a treatment in adding (quality of) life expected where each year following the treatment is given a weighting between 0 and 1 with 1 being perfect health and 0 being death. A sum of these years is taken.
Define Incremental Cost-Effectiveness Ratio (ICER)
The cost of a treatment divided by the QALY.
How much is a human year worth to the NHS in treatment costs?
The NHS will pay £30,000 per QALY (this can go higher for end-of-life drugs).
