Flashcards in Biostats Deck (34):
What is the equation for sensitivity?
What does 100% sensitivity indicate?
Low false negative rate
What is sensitivity used for?
Used for screening in diseases with low prevalence
What is the equation for specificity?
What does 100 percent specificity indicate?
A low false positive rate
What is the equation for positive predictive value?
What is the positive predictive value?
Probability that person actually has the disease given a positive test result
What is negative predictive value?
The probability that a person is actually drug free given a negative test result
What is the equation of negative PPV?
What is the true positive rate?
What is the true negative rate?
What is the equation for calculating incidence?
Number of new cases/number of people in population at risk (don't already have the disease)
What is the equation for prevalence?
Number of cases in a population/total number of people in the population
What is the equation for odds ratio?
Used in case-control studies (outcome --> exposure)
What is the equation for relative risk?
What is relative risk?
Risk among exposed/risk among unexposed
What is the equation for absolute risk?
(A/a+b) - (c/c+d)
#of adverse events in tx/# of adverse events in placebo
What is the number needed to treat?
The number of patients who need to be treated for 1 patient to benefit
What is the equation for the number needed to treat?
1/ (event rate -control) - (event rate - tx)
What is the number needed to harm?
Number of patients who need to be exposed to a risk factor for 1 patient to be harmed
What is the equation for the number needed to harm?
1/attributable risk = 1/(a/a+b) - (c/c+d)= 1/((RR-1)/RR)
What is the equation for event rate?
#of subjects per tx/total # of subjects
What is precision?
The consistency, reproduciblity and reliability of a test
What lowers precision?
What is accuracy of a test?
Absence of systematic error
What is the equation for SEM?
SD / square root sample size
So as sample size increases, standard error of mean decreases
What is the null hypothesis?
Says there is no difference btween two groups
P = high
What is the p-value?
The likelihood of observing what we did if the null is true.
The lower the p-value the more evidence for the alternative hypo
What is a type I error?
False positive error
Stating there s a difference when there really isn't.
P-value is judged against this
Ex: convicting an innocent man
What is a type II error?
Stating there isn't an effect or different when there is one
False negative error
Ex: Setting a guilty man free
What is power?
The probablility of seeing a difference when one is there
Ex: convicting a guilty man
= 1- B
What does power increase with?
Expect effect size
Precision of measurement
What is the equation for confidence interval?
Mean - Z(SEM) to mean + Z(SEM)
Z= 1.96 for 95% CI
Z = 2.58 for 99% CI