1. Descriptive Statistics & SPSS introduction
Nan Yu
COMM 420.8

2. Basic steps in conducting research
Literature review
Raise questions or make hypotheses
Design of a study
Collect evidence (qualitative evidence or quantitative evidence)
Analyze your evidence (data)
Draw conclusion from the analysis

3. Tasks for the next part of your group project
Collect evidence
Analyze your data
Results and Conclusion
Prepare for the presentation

4. Data Analysis Requirement Recommendation Understand statistics
Be able to use statistical software
Recommendation
Take other stat classes or data analysis classes if you are truly interested in this area.
This class will review very basic skills and principles about data analysis

5. A review – levels of measurement
Nominal/Categorical
e.g. Gender, Race, Favorite Music Genre
Ordinal
In a typical month, how many movies do you rent on video?
None
1-2
3-5
5-20
More than 20

6. Strongly Disagree Neutral Strongly Agree
Interval/Ratio
I believe in love at first sight.
Strongly Disagree Neutral Strongly Agree
On a typical day, how many hours of television do you watch?_______
How many siblings do you have?______

7. Text Book p.327, Table 14.1 Descriptive statistics
--reduce and simplify the number to interpret the results
Inferential statistics
--make a judgment of what you observe in the sample can be generalized to the population from which the sample was drawn

8. Text Book p.327. Table 14.1 Nonparametric Parametric (continuous)
Nominal, Ordinal
Parametric (continuous)
Interval, Ratio

9. Text Book p.327. Table 14.1 Univariate Bivariate Multivariate
One variable
Bivariate
Two variables
Multivariate
Three or more variables
Note: Sometimes scholars combine bivariate and multivariate so the distinction would be one variable (univariate) versus multiple variables (multivariate)

10. Descriptive Stats What to describe? What is the “center” of the data?
How the data vary? (variability)

11. Measures of central tendency
Mean
Mode
Median

12. Mean Another name of average
If describing a population, denoted as μ, the Greek letter “mu.”
If describing a sample, denoted as,
called “x-bar.”
“Balance point” or the “value center” of the distribution.
Only use for interval/ratio.

13. Calculating the Mean
Imagine that we have a population of 5 objects with heights of 2, 4, 6, 8, and 10 inches.
X1 = X2 = X3 = X4 = X5 = 10
The mean of the population is:
Sum of all the numbers divided by the number of observations contributing to that sum

14. Most frequently occurring score in a distribution.
Mode
Most frequently occurring score in a distribution.
One data set can have many modes.
Appropriate for all types of data, but most useful for categorical data.

15. Mode Hometown Number of students What is the mode in this case?
Pennsylvania
New York
New Jersey
Ohio
Maryland
Other States
What is the mode in this case?

16. Median Middle score in a distribution (50% above, 50% below)
Can use with ordinal and interval/ratio, but not with nominal

17. Median E.g., Scores: 4 9 2 2 1 8 10 9 7 Rank order them:
Rank order them:
Median

18. Summary
Choice of descriptive measures depends entirely on the level of measurement for a particular variable.

19. A normal distribution Symmetric, bell-shaped curve.
Most values fall around the mean, but some values are smaller, and some are larger.
mean
median
mode

20. But distributions are not always normal (p.345)
Skewness: How far the peak is from the center of the distribution

21. What happens if the distributions are not normal?
Impact of skewness on measures of Central Tendency
Mode
Mode
Median
Median
Mean
Mean
Right (Negative) Skew
Left (Positive) Skew

22. Distribution Kurtosis (p.345)
Normal (bell-shaped)
peaked
flat

23. Dispersion The mean, mode and median are not enough to understand the distribution of a variable.

24. Variability How variable are the scores in a distribution? Range
Standard Deviation
Variance

25. Range

26. Standard Deviation
A measurement of variability that indicates how much all of the scores in the distribution typically deviate from the mean.

27. Calculating Standard Deviation

28. Variance

29. What is the standard deviation for this distribution?

30. SPSS Statistical Package for the Social Science
A list of other available statistical software, p.332
Please download the file “Class Survey” from ANGEL (week 9) and save it on your desktop

31. Introduction to SPSS Opening a data file
STEP 1 Double click on the “class survey.sav” file.
STEP 2 Select "Edit," then "Options"
STEP 3 Select "Display names" and "File," then Click "OK"

32. Introduction to SPSS
Variables
Cases
(People)

33. Variable Labels To See Value Labels Place cursor over variable name
Click Value Label button

34. Sorting Cases Click Data -> Sort Cases
Select Variable, Move to Right Box, Click on OK when ready.

35. Data Editor in Variable View
Information About
Each Variable Across
Variables Listed
Down
Values

36. Frequencies/Descriptive Statistics
Requesting frequencies
Analyze -> Descriptive Statistics -> Frequencies

37. Select the variables you
want to analyze, and use
the arrow keys to move them
into the "Variables" box.
Click "Statistics."
Select the statistics you want,
and then click "Continue"
and then "OK."

38. Output Window
You can double-click on the chart and edit the appearance… You can copy and paste the chart into other applications...
Notice the new window...

39. Graphs A. Select "Graphs" then "Histogram"
B. Put “tvhours" in the variable box.
C. Select "Display normal curve" D. Select "OK"

40. In Your Output Window
You can double-click on the graph and edit the appearance. You can copy and paste the graph into other applications.

41. In Your Output Window
As new procedures are run, they are appended to the output and added to the outline on the left of the screen. You can navigate around your output by selecting from the outline menu. You can also delete any output by selecting it and then clicking the delete key.

42. Entering Your Own Data
A. Open Data (Type in Data)

43. Label for the Variables Variable Names Listed Down
B. Go to “Variable View” and name and label variables
Label for the Variables
Variable Names Listed Down
(No spaces)
Labels for the Values
Values Dialog Box: Click “Add” after each new value label that you include.

44. C. Enter data in “Data View”
Cell Editor
Case
Cell
1. Click on a given cell where you want to add data. 2. Type the value you want to include in that cell. The value will appear in the cell editor. 3. The TAB key will take you to the next variable in the same case. 4. The ENTER (return) key will take you to the next case.

45. D. Save your data after each case
I lost all my data
because I forgot
to save it.
Oh-my-gosh!
I think I forgot
to save the data!
Ha ha ha.
Too bad for them.
My data is safe!

46. Saving Your Data and Output
Extensions Used for File Types Date Files: .sav e.g., "mydata.sav" Output Files: .spo e.g., "myoutput.spo"

47. Saving Your Data File
A. From within the Data Editor, select "File" then "Save as" B. Select your floppy disk. C. Type in the name of your data file (with the extension .sav). D. Select "Save." Note: After you have saved your data for the first time, you can save it periodically by selecting "Save" rather than "Save as."

48. Saving Your Output File
A. From within the Output window, select "File" then "Save as" B. Select your floppy disk. C. Type in the name of your output (with the extension .spo). D. Select "Save." Note: After you have saved your output for the first time, you can save it periodically by selecting "Save" rather than "Save as."

49. Z-scores
If two measures were used to measure the liking toward “Nan Yu”
not likable likable
not nice nice
The raw scores are not comparable because they are measured differently.

50. So we need to standardize the scores…
What we do is…
Translating each individual score. The transformed scores will necessarily have a mean of zero and a standard deviation of one.
The standard score indicates how many standard deviations an observation is above or below the mean.

54. -3 -2 -1 1 2 3

55. Requesting Z-scores from SPSS
Open Class Survey.sav
Go to Analyze  Descriptive Statistics  Descriptive

56. Z-scores in SPSS A. Put “tvpm" in the variable box.
B. Check “Save standardize values as variables, can click OK

57. Z-scores in SPSS

58. Practice Request z-scores for “tvsit.”
Sort “Ztvsit” in a descending order.

59. In-Class Demo Run frequencies on “wwwbuy”
Request mean, median, mode, standard deviation, range, and skewness, and historgram with normal curve.
Does it look at a normal distribution? Base on the reported mean, median and mode, explain the skewness of the distribution of “wwwbuy.”

60. In-class Demo answer
You can compare your SPSS output with the one on ANGEL (class demo answer.spo)
No, it doesn’t look at a normal curve. The mean is higher the median and the mode. So it is a positive (left) skew.