Biostatistics

Random variable

takes a particular outcome by chance. Its behavior follows a probability distribution.

Expectation

the sum of the expected values

Variance

the sum of squared deviations divided by the number of observations minus 1; how far data spreads out from the mean

Probability distribution

a list of all the possible outcomes of a random variable along with their corresponding probability values.

Sensitivity

the probability of a positive test result when disease is present

Specificity

the probability of a negative test result when disease is absent

Positive predictive value (PPV)

the probability that disease is present when a test result is positive

Negative predictive value

the probability that disease is absent when test results are negative

Type I error

a false positive when you reject a true null hypothesis

Type II error

a false negative when you fail to reject a false null hypothesis

t-statistic

how far a sample mean is from a population mean, but we do not know the standard error

Z-statistic

how far a sample mean is from a population mean (in units of standard error)

Z-score

how far one observation is from the population mean

Critical value

a predefined threshold or cut-off point on a statistical distribution that separates the region of rejection from the region of non-rejection for a null hypothesis