Statistics Flashcards
how to calculate positive predictive value
TP / (TP + FP)
how to calculate negative predictive value
TN / (TN + FN)
How to calculate sensitivity
TP / (TP + FN )
Proportion of patients with the condition who have a positive test result
How to calculate specificity
TN / (TN + FP)
Proportion of patients without the condition who have a negative test result
What is the p value
is the probability of obtaining a result by chance at least as extreme as the one that was actually observed, assuming that the null hypothesis is true
What is confounding bias
occurs when there is a causal relationship between an unaccounted factor and the main outcome
What type of study are forest plots used in
meta analysis
how do forest plots display data
can be used to present and combine data from more than one study
what is recall bias
Difference in the accuracy of the recollections retrieved by study participants, possibly due to whether they have disorder or not.
particular problem in case-control studies
what is Publication bias
Failure to publish results from valid studies, often as they showed a negative or uninteresting result.
what is Expectation bias
in non-blinded trials. Observers may subconsciously measure or report data in a way that favours the expected study outcome.
what is the Hawthorne effect
Describes a group changing it’s behaviour due to the knowledge that it is being studied
what is Lead-time bias
Occurs when two tests for a disease are compared, the new test diagnoses the disease earlier, but there is no effect on the outcome of the disease
clinical trial phases?
phase 0 - exploratory studies
phase 1 - safety assessment
phase 2 - assess efficacy
phase 3- assess effectiveness
phase 4 - Postmarketing surveillance
clinical trial phase 0?
exploratory studies
very small number of participants and aim to assess how a drug behaves in the human body. Used to assess pharmacokinetics and pharmacodynamics.
help in determining whether it is feasible to move on to further phases
clinical trial phase 1?
safety assessment
Determines side-effects prior to larger studies. Conducted on healthy volunteers
clinical trial phase 2
assess efficacy
Involves small number of patients affected by particular disease
May be subdivided into
IIa - assesses optimal dosing
IIb - assesses efficacy
clinical trial phase 3?
assess effectiveness
Typically involves 100-1000’s of people, often as part of a randomised controlled trial, comparing new treatment with established treatments
clinical trial phase 4?
post marketing surveillance
Monitors for long-term effectiveness and side-effects
what is the confidence interval
a range of values within which the true effect of intervention is likely to lie
what is the confidence level
likelihood of the true effect lying within the confidence interval is determined by the confidence level.
example a confidence interval at the 95% confidence level means that the confidence interval should contain the true effect of intervention 95% of the time.
what can linear regression be used for
linear regression may be used to predict how much one variable changes when a second variable is changed
what is regression in terms of correlation
Once correlation between two variables has been shown regression can be used to predict values of other dependent variables from independent variables
what is a significance test
A null hypothesis (H0) states that two treatments are equally effective (there is no difference).
A significance test uses the sample data to assess how likely the null hypothesis is to be correct.
