This document provides definitions and formulae for measures of central tendency including arithmetic mean, weighted arithmetic mean, mean for ungrouped and grouped frequency tables, median, mode, geometric mean, harmonic mean, and their relationships. It was prepared by Medha Kulkarni as part of a series explaining descriptive statistics formulae on measures of central tendency. Contact information and social media links are provided for further resources.
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Descriptive statistics formulae Part I
1. Descriptive Statistics Formulae
Part I -
Measures of Central Tendency
Prepared By:
Medha Kulkarni
Email: medha.dataanalyst@gmail.com
Linkedin: http://in.linkedin.com/in/statsanalyst
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∑ fi, N n xi
r R2 α
β……
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ARITHMETIC MEAN
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Arithmetic
Mean
Add the values of all the observations.
Divide the above sum by the total number of
observations.
This calculated value is Mean
If x1, x2, x3…..xn are n observations, then
mean = (x1+x2+x3+…..xn)/ n
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WEIGHTED ARITHMETIC MEAN
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Weighted
Mean
The Weighted Arithmetic Mean of a set of
numbers x1, x2, ... xn, with corresponding
weights w1, w2, ...,wn, is,
n
nn
w
wwww
xwxwxwxw
x
....
.....
321
332211
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MEAN FOR UNGROUPED FREQUENCY
TABLE Follow @letstalkstatistics
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Mean for
ungrouped
data
Mean for an ungrouped frequency distribution
is calculated using the formula:
where fi is the frequency of the variable xi
Mean =∑fi xi
∑fi
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MEAN FOR GROUPED FREQUENCY TABLE
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Mean for a grouped frequency distribution is
calculated using the formula:
where fi is the frequency of the variable xi
xi is the class mark of the corresponding class
Mean =∑fi xi
∑fi
Mean for
grouped
data
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MEDIAN
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Median
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Middle value in the ordered data set.
Arrange the data in ascending or descending
order.
If number of observations are odd then
[(n+1)/2]
item is Median.
If number of observations are even then
average of {(n/2)th item + [(n/2)+1]th item} will
be Median.
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MEDIAN FOR UNGROUPED FREQUENCY
TABLE
Find N/2 where N= ∑fi
Check cumulative frequency just greater
than N/2
Corresponding x value is Median
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Median for
Ungrouped
Table
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MEDIAN FOR GROUPED FREQUENCY TABLE
Median = L + h ( N - c )
f 2
Median class = class corresponding to cumulative
frequency (cf) just greater than N/2
L = lower limit of median class
f = frequency of median class
h = width of median class
c = cf of the class preceding the median class
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Median for
Grouped
Table
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MODE FOR UNGROUPED FREQUENCY
TABLE Follow @letstalkstatistics
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Mode for
Ungrouped
Table
Mode for ungrouped frequency table is the value
that has the maximum frequency.
Data can have more that one mode.
Data with one mode value is called uni-modal, with
two modes is called bi-modal & with more than
two modes is called multi-modal.
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MODE FOR GROUPED FREQUENCY TABLE
Mode = l + {h(f1-f0) /(f1-f0)-(f2-f1)}
OR
Mode = l +{h( f1 – f0 )/( 2f1 – f0 – f2 )}
Modal class = the class interval with the largest
frequency.
l = lower limit
h = width
f1 = frequency of modal class
f0 = frequency of class preceding modal class
f2 = frequency of class succeeding modal class
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Mode for
Grouped
Table
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EMPIRICAL RELATION BETWEEN MEAN,
MODE & MEDIAN Follow @letstalkstatistics
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Empirical
Rule
(Mean –Mode) = 3*(Mean-Median)
Mode = 3Median – 2Mean
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GEOMETRIC MEAN
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Geometric
Mean
The Geometric Mean (GM) of n observations is
the nth root
of the product of the n observations.
GM x x x xnn ( )*( )*( ). .. *( )1 2 3
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GEOMETRIC MEAN FOR GROUPED TABLE
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Geometric
Mean for
grouped data
The Geometric Mean (GM) of n non-zero &
positive observations is given by
where values have
frequencies.
Nn
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Nf
n
ff in
xxxxGM
1
1
1
21
21
nxxx ,........,, 21
nfff ,.......,, 21
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WEIGHTED GEOMETRIC MEAN
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Weighted
Geometric
Mean
The Weighted Geometric Mean of a set of
numbers x1, x2, ... xn, with corresponding
weights w1, w2, ...,wn, is,
G.Mw =
where N = i.e. sum of weights
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HARMONIC MEAN
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Harmonic
Mean
The harmonic mean (HM) is the number of
variables divided by the sum of the reciprocals
of the variables.
where n = total number of observations
n
i ix
n
HM
1
1
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HARMONIC MEAN FOR GROUPED DATA
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The harmonic mean (HM) for grouped data is
given by
where fi is the frequency of the variable xiHarmonic
Mean for
Grouped
Data
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WEIGHTED HARMONIC MEAN
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Weighted
Harmonic
Mean
The Weighted Harmonic Mean of a set of
numbers x1, x2, ... xn, with corresponding
weights w1, w2, ...,wn, is,
where n = sum of weights
nn
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xwxwxw
n
HM
/....// 2211
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RELATION BETWEEN ARITHMETIC MEAN,
GEOMETRIC MEAN & HARMONIC MEAN
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AM, GM,
HM
For positive numbers