lesson 3 in spss how to find measures variability using spss
TRANSCRIPT
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Lesson 3 in SPSS
How to find measures variability using SPSS
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The Dataset
• Here’s a nice dataset.
• We have one variable called Age.
• There are 1,514 observations in the dataset.
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First Blush• To get a quick
picture of this dataset, let’s see a frequency distribution histogram (Lesson 1).
• Hmm, perhaps a bit skewed?
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Selecting the Analysis
• From the SPSS menu bar, choose
• Analyze
• Descriptive statistics
• Frequencies
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Select the Variable(s)
• In the Frequencies box, highlight the variable age, then click on the arrow to pop it into the Variables window.
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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.
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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.
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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.
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Running the Analysis
• Now we can click on OK.
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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 Respondent1514
3
45.63
41.00
35
17.808
317.140
.524
.063
71
18
89
69078
32.00
41.00
60.00
Valid
Missing
N
Mean
Median
Mode
Std. Deviation
Variance
Skewness
Std. Error of Skewness
Range
Minimum
Maximum
Sum
25
50
75
Percentiles
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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. Don’t worry about that now, we’ll look at this again in Lesson 4.
Statistics
Age of Respondent1514
3
45.63
41.00
35
17.808
317.140
.524
.063
71
18
89
69078
32.00
41.00
60.00
Valid
Missing
N
Mean
Median
Mode
Std. Deviation
Variance
Skewness
Std. Error of Skewness
Range
Minimum
Maximum
Sum
25
50
75
Percentiles
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Visual Representation
• Let’s mark these on our graph.
Mean
Median
Mode
Range = 71
Mean
s = 17.81SIQ = 14