I. FUNDAMENTALS -- A. Statistics and Methods Flashcards
Mean
A measure of central tendency. The arithmetic average of a sample or population, or the expected value of set of probabilities.
Formula of Sample Mean
Formula of Population Mean
Formula of Expected Value of a Set of Probabilities
Median
A measure of central tendency. The value at the 50th percentile (midpoint) of a sample or population.
Mode
A measure of central tendency. The value that occurs most frequently in a sample or population.
Standard deviation
A measure of spread of a sample, population, or set of probabilities. The square root of variance. Empirical rule says that, for a normal distribution, approximately 68% of observations are within +/- 1 standard deviation of the mean, and approximately 95% of observations are within +/- 2 standard deviations of the mean.
Formula of Sample Standard Deviation
Formula of Population Standard Deviation
Formula of Standard Deviation of a Set of Probabilities
Variance
A measure of spread of a sample, population, or set of probabilities. Standard deviation squared. Cannot be negative.
Formula of Sample Variance
Formula of Population Variance
Formula of Variance of a Set of Probabilities
Covariance
A measure of how things move together. Just a directional measure (positive value means that things move in the same direction and negative value means that things move in opposite directions).
Correlation
A measure of how things move together. Between -1 and +1. Indicates the strength of the relationship.
Skewness
A departure from the normal distribution.
Left or negatively skewed is where mean < median < mode.
Right or positively skewed is where mean > median > mode.
Stock returns are positively skewed due to survivorship bias.
Standard deviation overestimates risk for negatively skewed distributions and underestimates risk for positively skewed distributions.

Range
The difference between the largest and smallest value in a sample or population.
Absolute Deviation
Mean absolute deviation is the average of the absolute values of differences between each value and a measure of central tendency. The measure of central tendency used can be the mean, median, or mode.
Semi-variance
Variance formula but only including observations below the mean or other target value (such as MAR or minimum acceptable return).
Normal distribution
Symmetric: the probability of any positive devation above the mean is equal to that of a negative deviation of the same magnitude.
Stable: when assets with normally distributed returns are mixed to construct a portfolio, the portfolio return is also normally distributed.
Only two parameters – mean and standard deviation – need to be estimated to obtain the probabilities of future scenarios.
When securities are normally distributed, the statistical relation between returns can be summarized with a single correlation coefficient.