stats Flashcards
what is randomised controlled trial?
participants randomly allocated to intervention or control group (e.g. standard treatment or placebo)
Practical or ethical problems may limit use
what is 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.
usual outcome measure for cohort sutdy?
relative risk
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.
Inexpensive, produce quick results
Useful for studying rare conditions
Prone to confounding
usual outcome measure in case-control study?
odds ratio.
cross-sectional survey?
Provide a ‘snapshot’, sometimes called prevalence studies
Provide weak evidence of cause and effect
what is the gold standard in terms of evidence?
meta-analysis
what is meta-analysis?
a statistical technique used to combine data from multiple studies to derive a more precise estimate of a treatment effect or association
the primary goal is to increase power and improve estimates of the size of the effect, especially when individual studies may be too small (i.e. low-powered) to produce reliable results on their own
what can affect meta-analysis?
meta-analyses can be affected by publication bias, where studies with positive results are more likely to be published than those with negative or inconclusive results
what is variance?
how measures?
Variance is a measure of the spread of scores away from the mean.
Variance = square of standard deviation
how do you measure sensitivity?
TP / (TP + FN )
what is sensitivity?
Proportion of patients with the condition who have a positive test result
what is specificity?
Proportion of patients without the condition who have a negative test result
how do you measure specificity?
TN / (TN + FP)
what is positive predictive value?
measure?
The chance that the patient has the condition if the diagnostic test is positive
TP / (TP + FP)
what is negative predictive value?
measure?
TN / (TN + FN)
The chance that the patient does not have the condition if the diagnostic test is negative
what Is Likelihood ratio for a positive test result ?
measure?
sensitivity / (1 - specificity)
How much the odds of the disease increase when a test is positive
what is Likelihood ratio for a negative test result?
measure?
(1 - sensitivity) / specificity
How much the odds of the disease decrease when a test is negative
what is precision?
The precision quantifies a tests ability to produce the same measurements with repeated tests.
what is null hypothesis?
A null hypothesis (H0) states that two treatments are equally effective
what is the p value?
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 type 1 error?
the null hypothesis is rejected when it is true
what is type 2 error?
the null hypothesis is accepted when it is false
what is the power fo a study?
The power of a study is the probability of (correctly) rejecting the null hypothesis when it is false, i.e. the probability of detecting a statistically significant difference
power = 1 - the probability of a type II error
power can be increased by increasing the sample size
