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Measures of
central tendency are statistics that tell us basic characterisitcs
about a set of data. These are single number
representatives of general characteristics of the group (not
individual cases withing hte group), often called averages.
For example, your course grade is a single number indicator of your
performance in the class (compiled from a set of data values such
as test, homework and paper scores). There are several types
of measures of central tendency. There are several types of averages,
and the savvy student learns which is the most appropriate for a
given context. The most common is the mean,
this is the statistic that is used to calculate your GPA, average
monthly temperatures, and the average daily balance on your credit
card. The mean is used when you have a set of
numerical data, such as test scores or incomes and you want to include
all values in your set of data. It is the sum of the data
values divided by the number of cases.
The median
is another type of "average" which is often confused with
the mean. The median is used when you are interested in knowing
the middle value of a set of data, and you do not want extreme
high or low value to distort your average (see the tutorial
for an example). Often the median provides a more realistic
representation of the central characteristics of a set of data than
the mean does. For example if you want to get a sense
of the "average income" on your middle- class street,
and someone who is exceedingly wealthy moves in next door, would
it make sense to factor his or her income into your calculation?
If you did, it would probably give a distorted picture of
the average person on your street. However, if you figured
the median income for the street, the unusually high income would
not distort the average nearly as much, and your statistic would
be a much better indicator of reality.
Mode
is yet another type of commonly used average which simply indicates
the most frequesntly occurring data value. For example, you
want to know what the "average" credit card is in the
US. What you really mean by this is "what is the most
commonly used credit card?" To answer this question you
cannot calculate the mean or median because your data is not numerical.
You can however figure the mode. If Debts-R-Us is the card
carried by the most people, then it is the "modal" or
"average" credit card.
Tutorial
for mean, median, and mode
Recommended
Link
Statistics Every Writer
Should Know. This is an excellent site that clearly explains
important concepts. A must see.
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