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.
Significance test types
depends if parametric (can be measured) or non-parametric
what is the alternative hypothesis
There is a difference between the two treatments
what are parametric studies and examples
significance test which is measurable, usually normally distributed
Student’s t test - paired or unpaired
Pearson’s product moment coefficient - correlation
What is the Pearsons test
parametric test, measurable
correlation between numeric variables
What is the student t test and difference between paired and unpaired
Parametric test
paired data refers to data obtained from a single group of patients, e.g. Measurement before and after an intervention.
Unpaired data comes from two different groups of patients, e.g. Comparing response to different interventions in two groups
What are non parametric test
significance test where cant be measured
Do not require a distribution to meet the required assumptions to be analysed
what is the man whitney u test
non parametric significance test
compares ordinal, interval, or ratio scales of unpaired data
what is the wilcoxon signed rank test
non parametric signif test
compares two sets of observations on a single sample, e.g. a ‘before’ and ‘after’ test on the same population following an intervention
what is the chi-squared test
used to compare proportions or percentages e.g. compares the percentage of patients who improved following two different interventions
what is the spearman kendall rank
non parametric test - correlation
what is a randomised control trial
Participants randomly allocated to intervention or control group (e.g. standard treatment or placebo)
Practical or ethical problems may limit use
what is a cohort study
observational and prospective
Two (or more) are selected according to their exposure to a particular agent (e.g. medicine, toxin) and followed up to see how many develop a disease or other outcome.
The usual outcome measure is the relative risk.
see what happens in future w exposure
what is a case-control study
Observational and retrospective.
Patients with a particular condition (cases) are identified and matched with controls.
Data is then collected on past exposure to a possible causal agent for the condition.
The usual outcome measure is the odds ratio.
what is a cross-sectional survey
Provide a ‘snapshot’, sometimes called prevalence studies
Provide weak evidence of cause and effect
