Stats Flashcards
Variance
Measures how far a set of numbers are spread out
Variance defined
average squared differences between the mean and each item in the population or in the sample
High variance means
data points are very spread out
Standard deviation defined
measure of dispersion expressed as the square root of the variance
Standard deviation measures
the amount of variability around the average or mean
Advantage of standard deviation
expresses dispersion in the same units as the original values in the sample or population
A low standard deviation indicates
data points gather close to the means
Semi variance measures
data that is below the mean or target value of a data set
Semi variance defined
average of the squared deviations of all values less than the average or mean
Coefficient of variation defined
ration of the standard deviation to the mean
CV formula
standard deviation/mean
CV result
shows the extent of variability of relation to mean of the population
CV application
for comparison of data sets with different units or widely different means, one should use the CV instead of SDEV
Skewness defined
describes asymmetry of data points from a normal distribution
Negative skew
skews to the left
Positive skew
Skews to the right
Non-normal distributions (Skewness applied)
standard mean-variance analysis is limited which means SDEV is less meaningful
For a negative skew - SDEV applications
underestimating the risk
For a positive skew - SDEV applications
overestimating the risk
Kurtosis measures
How fat the tails are on a distribution relative to a normal distribution curve
Positive Kurtosis (Leptokurtic)
will show more extreme outcomes, creating a tendency for the observations around the mean to seem great and appearing to have a higher peak
Low Kurtosis (Platykurtic)
will show thinner tails (fewer extreme outliers), flatter top, less peakedness
Higher kurtosis suggest greater
Risk than reflected in the normal distribution relied upon in the traditional mean-variance framework
Standard deviation is a good measure of risk when returns are
symmetric
What if excess returns are not normally distributed
Standard deviation is no longer a complete measure of risk; Sharpe ratio is not a complete measure of performance; need to consider skew and kurtosis
N vs. N-1
Use N when you are using all of the data available (I.e. Population) then use N-1 when only using a sample (I.e. calculating standard deviation)