ANOVA

1
ANOVA

• Richard Rivera
• (aka Rico)

2
ANOVA

• In this lesson I will kill two birds with one
  stone. Youll be introduced on how to
• import excel data files into SPSS
• conduct analyses of variance in SPSS

3
Need some Data Files

• But first, you need to download an Excel data
  file.
• Open up your internet Explorer
• Copy and paste the following two links into the
  web browser.
• http//www.west.asu.edu/statlab/downloads/Workshop
  Example.xls
• http//www.west.asu.edu/statlab/downloads/Workshop
  Example.sav
• Please save them to your Desktop.

4
Two Topics

• Prepping an Excel spreadsheet to be imported into
  SPSS
• Types of Analyses of variance (ANOVA).

5

• Excel spreadsheet
• Each column is indicative of a variable
• First row contains the variable names
• You want to keep the same rules that apply to
  variable names in SPSS
• The subsequent rows contain the data for each
  case (subject)
• Gender has two levels
• Male 1
• Female 2
• Age has three levels
• lt 25 1
• 25 - 40 2
• gt 40 3
• Time has three levels
• Baseline time0
• Time 1 time1
• Time 2 time2
• Composite scores for attitude towards research

6

• Excel spreadsheet
• I sorted the data based on gender and age
  variables for instructional purposes.

7

• Between subjects (aka independent samples)
• What are two between-subject factors that have
  independent samples?
• Gender 2 samples
• Age 3 samples
• Within subjects (aka related samples)
• What is the one within-subject factor that is
  indicative of three related samples?
• Time 3 samples

8
Importing Excel Data into SPSSStat Lab Staff
you may want to print this slide and follow the
SPSS directions below

• After formatting the data in Excel
• First row contains the variable names
• Other rows contain the data values
• Save and close Excel file
• Open up SPSS
• Click on File gt Open gt Data
• Navigate to the location you save the Excel file
• In Files of type choose either
• Excel (.xls)
• or All files (.)
• Open the Excel file you saved
• Youll get a dialogue box called Opening Excel
  Data Source
• There is a green check mark in box Read variable
  names from the list from the first row of data
• Worksheet choose the worksheet in which the data
  is located
• Click the OK button.
• You just imported an excel file into SPSS

9
Analysis of Variance

• One-way ANOVA
• One between subjects factor
• Example Age (discrete variable)
• Two-way ANOVA
• Usually consist of two between subjects factors
• Example Age and Gender
• Repeated Measures
• One-way within subjects ANOVA
• One within subjects factor
• Example Time
• Two-way between and within subjects ANOVA
• One between subjects factor (e.g., Age)
• And one within subject factor (e.g., Time)

10
One-way ANOVA

• You may want to open the SPSS data file that you
  downloaded.
• Differences among 2 or more independent sample
  means with SPSS
• Analysis of Variance between subjects factor
• Analyze gt Compare Means gt One-Way ANOVA
• One dependent variable (e.g., baseline, time0)
  goes into the Dependent List
• One between subjects factor (e.g., Age) goes into
  Factor
• If the factor has more than three level, click on
  Post Hoc
• Click on Tukey and Dunetts C (unless your
  instructor wants you to use a different one).
• Click on continue
• Click on Options
• Chose
• descriptive Statistics
• Homogeneity of variance test
• Perhaps on Means plot
• Click on continue
• Click on OK

11
Descriptive Statistics

• The first column contains the three levels of
  the Age factor.
• The mean column contains the mean attitude
  toward statistics
• Does it appear that there may be an age effect?
• Do you notice a trend?
• Which age group has the greatest mean?

12
F-test

• The F-test looks tells us if there is an age
  effect.
• Is the F-test significant?
• Look at the p value (in column called Sig.)
• Is it less than an alpha of .05?
• However, the F-test does not tell us which pair
  of means are significantly different.
• We look at the multiple comparisons for that.

13
Multiple Comparisons

• Mean difference column was calculated by
  subtracting the means for age categories in
  column (j) from means for age categories in
  column (I).
• If there is an asterisk, the mean difference is
  significant.

14
Two-way ANOVA

• Example two between subjects factors
• Analyze gt General Linear Model gt Univariate
• Dialogue box titled Univariate
• Dependent variable move one dependent variable
  (e.g., baseline time0)
• Fixed Factor(s) move in the between subjects
  factors (e.g., Gender and Age).

15
Dialogue box titled Univariate(continued)

• Click on Plots
• Move one of factors into horizontal axis and the
  other into separate lines
• Click Add
• If you wish, you can do the inverse of that, then
  click add again
• Click Continue

16
Dialogue box titled Univariate(continued)

• Click on Post Hoc
• Choose only factors that have three or more
  levels. (e.g., Age).
• Click on Tukey and Dunetts C (unless your
  instructor wants you to use different ones).
• Click on continue

17
Dialogue box titled Univariate(continued)

• Click on Option
• Choose Descriptive statistics
• Homogeneity tests
• Click on continue
• Click on OK

18
Repeated Measures

• Within Subjects ANOVA example
• Analyze gt General Linear Model gt Repeated
  Measures
• Dialogue box Repeated Measures Define Factor(s)
• Within-Subject Factor Name
• Change name to time
• Number of levels 3 levels (i.e., baseline,
  time0, and time1)
• Click on Add
• Click on Define

19
Dialogue Box Repeated Measures

• Within-Subjects Variables (time)
• Choose the three variables (time0, time1, time2)
  the insert them in the correct order.
• Between-Subjects Factor(s)
• Insert the factors that you are interested in.
• In this case, enter in Age.

20
Dialogue Box Repeated Measures(continued)

• Click on Plots
• I recommend that you move the Time factor into
  horizontal axis and the other (Age) into separate
  lines
• Click Add
• Click Continue

21
Dialogue Box Repeated Measures(continued)

• Click on Post Hoc
• Choose only factor(s) that have three or more
  levels. (e.g., Age).
• Click on Tukey and Dunetts C (unless your
  instructor wants you to use different ones).
• Click on continue

22
Dialogue Box Repeated Measures(continued)

• Click on Option
• Choose Descriptive statistics
• Homogeneity tests
• Click on continue
• Click on OK

23
Results Coach

• In many instances there is a results coach in
  SPSS for certain types of output.
• In the SPSS output, you can right click on a
  table and choose results coach
• Results coach, which uses an example from a
  different data set, will introduce you to some of
  the concepts in the tables.
• Good luck!