M5 Flashcards
are measures of the
average distance of each observation from the center of the
distribution.
Measures of Variability or Dispersion
tell us how spread out
the scores are
Measures of Variability or Dispersion
summarize and describe the extent to which scores in
a distribution differ from each other.
Measures of Variability or Dispersion
two general classifications of Measures of
Variability or Dispersion:
1) Measures of absolute dispersion
2) Measures of relative dispersion
cannot be used to compare variations of two data sets when
the averages of these sets differ a lot in value or when the
observations differ in units of measurements.
measures of absolute dispersion
are expressed in the units of the original observations
measures of absolute dispersion
This is the simplest but most unreliable measure of
dispersion since it only uses two values in the distribution
range
is the difference between the highest and the lowest values.
range
is the average of the squared deviation of each score from the
mean
variance
is the square root of the average of the squared deviation of each score from the
mean, or simply, the square root of the variance
standard devation
are unitless measures and are used when one wishes to
compare the scatter of one distribution with another
distribution.
measures of relative dispersion
is the ratio of the standard deviation to the mean and is
usually expressed in percentage.
coefficient variation
is used to compare
variability of two or more sets of data even when they are
expressed in different units of measurements.
coefficient variation
At least the fraction of 1 β 1/π^2
of measurements of any set of
data must lie within π standard deviations of the mean.
chebyshevβs theorem
are values
below which a specific fraction or percentage of the observations
in a given set must fall.
fractile or quartile