1. Path Analysis in SEM

2. Final Project December 17 No class but final paper due
Please submit hard copy of paper in mailbox (1008)
Can schedule SPSS/AMOS assessment during this time
Next week – help session (stop by with any questions about final project, etc) – Optional session?

3. Keep in Mind... Same assumptions hold for path analysis Linearity
Independent observations
Errors normally distributed & relatively constant

4. Additional Assumptions
Disturbances uncorrelated with IVs
There is no reverse causation
The exogenous variables are perfectly measured
A state of equilibrium (enough time has elapsed for cause to take effect)
All common causes of presumed cause & presumed effect included

5. Dangers of Path Analysis
Omitted common cause
Biggest danger (misspecification), aka spurious correlation
Common causes, not all causes
Paths in the wrong direction
Unreliability and invalidity

6. Spurious Correlation

7. Effects of Parental Involvement

8. PI Model (MR)

9. Neglected Common Cause
Without prior achv’t we overestimate effect of PI

10. Excluding a Non-Common Cause
Including all possible variables is not always a good idea! (reduce degrees of freedom)

11. The Power of True Experiments
Not a common cause!

12. Mediators are interesting but not necessary
What about mediators?
Total Effects
0.47
Mediators are interesting but not necessary

13. Paths in the Wrong Direction
Nothing to really indicated you’ve misspecified (although 10th grade GPA on 8th grade PI makes no sense)

14. Another Path in Wrong Direction
Direct effects are same but indirect and total effects differ

15. Steps in Path Analysis Think…Draw a tentative model
Study relevant theory & research
Which variables to include?
Causal direction?
Revise the model
Check ID status (prefer overidentified models)
Collect sample, measure variables
Estimate the model
Fill in the model estimates (is it as expected?)
Interpret, write up
Steps in Path Analysis

16. Using AMOS

17. Standardized Output Using AMOS

18. Unstandardized Output: AMOS

19. Detailed Output

20. Detailed Output

21. Total Effects

22. Direct Effects

23. Indirect Effects

24. Overidentified Model

25. Overidentified Model

26. Fit of Model

27. Determining “Fit”

28. Fit of the Model
TLI, CFI, AGFI > .90
RMSEA < .05

29. Fit of the Model You determine fit by looking at:
Chi-square statistic = measure of misfit, would prefer it to be not significant
Fit indices

30. Initial Model

31. Alternative Model

32. Comparing Models

33. MR or SEM? If just-identified or single model
Either MR or SEM (no real advantage to SEM)
If over-identified
SEM (fit statistics)
If comparing models

34. Another Example...

35. Another Example...

36. Final project Idea
The purpose of this assignment is to familiarize you with the SEM software, AMOS. Your task is to rerun the path analysis that you specified in SPSS using AMOS. For this model, describe the following:
Identification status of the model
Estimates of the model (compare these estimates to those generated by SPSS)
Overall fit of the model – what do the fit indices suggest? Does your model fit your data well or poorly?
Interpret your findings, including a discussion of possible alternative models
Now, using AMOS, run at least one alternative model. Compare your estimates and overall fit of the model to your original model. Please attach the AMOS output to your quiz.

37. AMOS
AMOS and SPSS are compatible; but AMOS prefers dataset with NO missing data
Start AMOS Graphics
Draw your diagram
Boxes = observed variables
Errors = unobserved variables for your DVs
Direct effects = straight lines
Covariances = curved lines between exogenous variables
Save your diagram (.amw = AMOS extension)

38. Another Example...

39. AMOS Useful tools to make your diagram look neater: Copy Touch up
Resize to fit diagram
Read your data into AMOS
FILE  Data Files  OK
Label your variables (both observed and unobserved)
Under analysis properties, select any additional information you want AMOS to generate:
Standardized estimates
Implied and sample moments
Modification indices (won’t run if you have missing data)
Click on calculate estimates