Stats Flashcards
How to interpret RR?
A risk ratio of 1.0 indicates identical risk among the two groups. A risk ratio greater than 1.0 indicates an increased risk of the occurrence of interest for the exposed group. A risk ratio less than 1.0 indicates a decreased risk for the exposed group.
How to calculate Relative Risk?
Exposed vs not exposed, yes outcome vs no outcome table
(a/a+b) / (c/c+d) OR
Experimental event rate / control event rate
Define:
true positive
false positive
true negative
false negative
PPV
NPV
Sensitivity
specificty
True positive [TP]: the number of cases correctly identified as having the disease.
False positive [FP]: the number of cases incorrectly identified as having the disease.
True negative [TN]: the number of cases correctly identified as healthy.
False negative [FN]: the number of cases incorrectly identified as healthy.
Positive predictive value: the proportion of cases with a positive test result who have the disease.
TP/(TP + FP)
Negative predictive value: the proportion of cases with a negative test result who do not have the disease
TN/(TN+FN)
Sensitivity: the proportion of people with the disease who have a positive test.
TP/(TP+FN)
Specificity: the proportion of healthy people who have a negative test.
TN/(TN+FP)
Define NNT
Number Needed to Treat (NNT) is the number of patients who must (on average) be treated with a specific therapy for one of them to benefit
Define NNH
Number needed to harm or NNH is a measure of the relative harm of an intervention - eg smoking. It is the inverse of the absolute risk increase
What is the standard NHS time period, after an adverse incident has occurred, by which a patient can lodge a complaint?
1 year
how to calculate the power of a study?
what does it mean?
1-beta/type 2 error
measures ability of a study to detect a true effect. greater power = greater chance of detecting true effect.
what is type 1 (alpha) error?
how to reduce
false positive error
stating there is an effect when there is none
can be reduced by insisitng on lower p value e.g. <0.01
what is type 2 (beta) error?
how to reduce
false negativeerror
stating there is an effect when there is none
can increase sample size
what does a symmetrical, inverted funnel mean in a funnel plot?
no publication bias
define primary prevention
reduce illness in population, reduce risk of new cases
secondary prevention
detect + treat pre symptomatic disease
tertiary prevention
reduce morbidity from existing conditions
A p-value of 0.01 is reported in a study testing the effect of a new antibiotic on the rate of infection. What does this mean?
There is a 1% chance that the observed results are due to random variation if the null hypothesis is true.
