Transcript Lesson 2 in SPSS

Lesson 3 in SPSS
How to find measures variability
using SPSS
The Dataset
• Here’s a nice
dataset.
• We have one
variable called
Age.
• There are 1,514
observations in the
dataset.
First Blush
• To get a quick
picture of this
dataset, let’s
see a
frequency
distribution
histogram
(Lesson 1).
• Hmm,
perhaps a bit
skewed?
Selecting the Analysis
• From the
SPSS menu
bar, choose
• Analyze
• Descriptive
statistics
• Frequencies
Select the Variable(s)
• In the
Frequencies
box, highlight
the variable
age, then click
on the arrow
to pop it into
the Variables
window.
Descriptives Box
• Notice that
when you’ve
done this, the
OK box is
now active.
• But let’s
make sure
we get the
statistics we
want.
Selecting the Statistics
• I’ve selected the
mean, median and
mode as my
measures of central
tendency. Plus, I
asked for the sum.
• For my measures of
spread, I’ve chosen
standard deviation,
variance, and range.
Plus I asked for the
minimum and
maximum values.
The Interquartile Range
• To find the
interquartile range in
SPSS, select
Quartiles.
• I’ve also asked it for a
measure of the
skewness of the
distribution.
• Now click on Continue.
Running the Analysis
• Now we can
click on OK.
The Output
•
•
•
•
So what did we learn?
The mode is 35, the
median is 41.00, and the
mean is 45.63. These
measures appear to be
the perfect definition of a
positively skewed
distribution.
The range is 71 and goes
from a minimum of 18
years to a maximum of 89
years old.
The sample variance is
317.14 and taking the
square root of that we
have the sample standard
deviation of 17.81
Statistics
Age of Respondent
N
Mean
Median
Mode
Std. Deviation
Variance
Skewness
Std. Error of Skewness
Range
Minimum
Maximum
Sum
Percentiles
Valid
Missing
25
50
75
1514
3
45.63
41.00
35
17.808
317.140
.524
.063
71
18
89
69078
32.00
41.00
60.00
More Output
• To find the interquartile range, we
take the 75th percentile minus the 25th
percentile. Here, it is
60 – 32 = 28. So the
SIQ = 28/2 = 14.
• Also, we note our
skewness value is
.524 with a standard
error of .063. Don’t
worry about that now,
we’ll look at this
again in Lesson 4.
Statistics
Age of Respondent
N
Mean
Median
Mode
Std. Deviation
Variance
Skewness
Std. Error of Skewness
Range
Minimum
Maximum
Sum
Percentiles
Valid
Missing
25
50
75
1514
3
45.63
41.00
35
17.808
317.140
.524
.063
71
18
89
69078
32.00
41.00
60.00
Visual Representation Median
Mode
• Let’s mark
these on
our graph.
Mean
Mean
SIQ = 14
s = 17.81
Range = 71