1
THE DATASET
Here’s a nice dataset.
We have one variable called Age.
There are 1,514 observations in the
dataset.
2
FIRST BLUSH
To get a quick picture of
this dataset, let’s see a
frequency distribution
histogram (Lesson 1).
Hmm, perhaps a bit
skewed?
3
SELECTING THE ANALYSIS
From the SPSS menu
bar, choose
Analyze
Descriptive statistics
Frequencies
4
SELECT THE VARIABLE(S)
In the Frequencies box,
highlight the variable
age, then click on the
arrow to pop it into the
Variables window.
5
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.
6
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.
7
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.
8
RUNNING THE ANALYSIS
Now we can click on OK.
9
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
10
MORE OUTPUT
To find the inter-quartile range, we
take the 75th per-centile 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.
By dividing the skewness by its
standard error, we get 0.524/0.063
= 8.317. What does this mean? You’ll
learn more about this in the next
lesson. For now, know that any value
greater than 3.3 or less than -3.3
indicates a high degree of skewness.
Yep, we’re skewed!
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
11
VISUAL REPRESENTATION
Median
Mode
Let’s mark these
on our graph.
Mean
Mean
SIQ = 14
s = 17.81
Range = 71
12