Transcript Basic Data Analysis: Descriptive Statistics

Basic Data Analysis:
Descriptive Statistics
Types of Statistical
Analysis
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Descriptive
Inferential:
 Test
of Differences
 Test of Associative
 Predictive
Pre Descriptive Statistics
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Data entry - Data coding (data code book).
Data matrix
Descriptive statistics - “describe” the data,
portray an average respondent (data
reduction):
 Summarizes
 Conceptualizes
 Communication
 Interpolation/extrapolation
Descriptive Statistics
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Statistical concepts:
 Measures
of Central Tendency
 Measures of Variability
 Other Descriptive Measures
Measures of Central
Tendency
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Applies to any measure that reflects a
typical or frequent response
Mode: the number that appears most often
Median: the value whose occurrence lie in
the middle of a set of numbers (half above
and half below)
Mean: arithmetic average of a set of
numbers
Measures of Central
Tendency
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Mean: arithmetic average of a set of numbers
X=sample mean
m = Population mean
Measures of Variability
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Reveal the typical differences between values
in a data set
Frequency Distribution: tabulation of the
number of times that each different value
appears in a data set, shown as a percentage
Range: difference between the lowest and
highest value in a data set
Measures of Variability
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Standard Deviation: indicates the degree
of variation or diversity in the values in
such as way as to be translatable into a
normal curve distribution
With a normal curve, the midpoint (apex)
of the curve is also the mean and exactly
50% of the distribution lies on either side
of the mean.
Normal, bellshaped curve
50%
50%
Midpoint
(mean)
Normal Curve and
Standard Deviation
Number of
standard
deviations from
the mean
Percent of area
under the curve
Percent of area to
the right or left
+/- 1.00 st dev
68%
16%
+/- 1.64 st dev
90%
5%
+/- 1.96 st dev
95%
2.5%
+/- 2.58 st dev
99%
0.5%
Other Descriptive
Measures
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Measures of skewness
 Is
the curve really bell-shaped or does it
“skew” to one side or the other?
 The closer the number given for skewness is
to zero, the closer the distribution is to being
bell-shaped.
 A positive skewness means that the
distribution has a tail to the right while a
negative skewness means it has a tail to the
left
Other Descriptive
Measures
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Kurtosis indicates how pointed or peaked the
distribution.
A kurtosis value of zero or close to zero
indicates that the distribution is bell-shaped.
When to use what
Type of
Measurement
Nominal
Ordinal
Interval/Ratio
Central Tendency
Mode
Median
Mean
Variability
Frequency or
percentage
distribution
Percentage
distribution
Standard
deviation
Microsoft Excel
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Menu: Tools, Data Analysis, Descriptive
Statistics
If Data Analysis is not present under Tools
Bar then
 go
to Tools, Add-ins
 check Analysis Toolpak and Analysis Toolpak
VBA
 click OK
 Data analysis should appear under Tools now