1. Educational Research: Causal-Comparative Studies
Richard M. Jacobs, OSA, Ph.D.

2. Research...
The systematic application of a family of methods employed to provide trustworthy information about problems
…an ongoing process based on many accumulated understandings and explanations that, when taken together lead to generalizations about problems and the development of theories

3. The basic steps of research...
Scientific and disciplined inquiry is an orderly process, involving:
 recognition and identification of a topic to be studied (“problem”)
 description and execution of procedures to collection information (“method”)
 objective data analysis
 statement of findings (“results”)

4. Research methods... Quantitative…
…collects and analyzes numerical data obtained from formal instruments

5. Quantitative methods... descriptive research (“survey research”)
correlational research
causal-comparative research (“ex post facto research”)
experimental research

6. causal-comparative research (“ex post facto research”)
…at least two different groups are compared on a dependent variable or measure of performance (called the “effect”) because the independent variable (called the “cause”) has already occurred or cannot be manipulated

7. Research variables... Independent…
…an activity of characteristic believed to make a difference with respect to some behavior
…(syn.) experimental variable, cause, treatment

8. dependent variable…
…the change or difference occurring as a result of the independent variable
…(syn.) criterion variable, effect, outcome, posttest

9. A causal-comparative study…
…a study in which the researcher attempts to determine the cause, or reason, for pre-existing differences in groups of individuals
…called an “ex post facto” study because both the effect and the alleged cause have already occurred and must be studied in retrospect

10. Differences in causal-comparison and correlational studies…
causal-comparative studies…
…attempt to identify cause-effect relationships
correlational studies…
…attempt to identify relationships

11. causal-comparative studies…
…involve two (or more) groups and one independent variable
correlational studies…
…typically involve two (or more) variables and one group

12. causal-comparative studies…
…involve making comparisons
correlational studies…
…involve establishing relationships

13. Differences in causal-comparison and experimental studies…
causal-comparative studies…
…individuals are not randomly selected but selected because they belong to groups
experimental studies…
…individuals are randomly selected and assigned to two (or more) groups

14. causal-comparative studies…
…the researcher cannot manipulate the independent variable
experimental studies…
…the researcher manipulates the independent variable

15. causal-comparative studies…
…the independent variable has already occurred and cannot be manipulated
experimental studies…
…the researcher manipulates the independent variable to determine its effects

16. causal-comparative studies…
…the random sample is selected from two already-existing populations
experimental studies…
…the random sample is selected from a single population

17. Conducting a causal-comparative study…
1. select the problem
2. select participants and instrument
3. design and procedure
4. data analysis and interpretation

18. 1. select the problem…
…the researcher starts with an effect and seeks its causes
…the independent variable cannot or should not be manipulated

19. 2. select the participants and instrument…
…select samples representative of their respective populations and similar with respect to critical variables other than the independent variable
…called “comparison groups”

20. 3. design and procedure…
…the performance of the groups is compared using some valid dependent variable measure (“instrument”)
…lack of randomization, manipulation, and control are sources of weakness

21. control
…the process by which the researcher attempts to ensure that the findings are as free of researcher bias and error as possible

22. types of control
…random assignment of participants to groups
…pair-wise matching
…comparing homogeneous groups
…comparing homogeneous subgroups
…factorial analysis of variance
…analysis of covariance

23. random assignment of participants to groups
…not possible in causal-comparative studies because the groups already exist and have already received the treatment

24. pair-wise matching
…first: find a participant in the second (third, fourth, etc.) group with the same or similar score on the control (nonmanipulated) variable as the participant in the first group
…second: if a participant in either group does not have a suitable match, the participant is eliminated from the study

25. comparing homogeneous groups
…control for extraneous variables that are homogeneous with respect to the extraneous variables
…limitation: lowers the number of participants in the study and, of course, limits the generalizability of the findings

26. comparing homogeneous subgroups
…form subgroups within each group that represent all levels of the control (nonmanipulated) variable
…controls for the variable and also permits the researcher to determine whether the independent variable affects the dependent variable differently at different levels of the control (nonmanipulated) variable

27. factorial analysis of variance (“FANOVA”)
…building the control (nonmanipulated) variable into the research design
…then use FANOVA to analyze the results to determine the effect of the independent and control (nonmanipulated) variable on the dependent variable, both separately and in combination

28. …FANOVA allows the researcher to determine if there is an interaction between the independent variable and the dependent variable such that the independent variable operates differently at different levels of the independent variable building it into the research design

29. analysis of covariance (“ANCOVA”)
…statistically adjusts initial group differences on a dependent variable for initial differences on some other variable related to performance on the dependent variable
…removes initial differences so that the results can be fairly compared as if the two groups started equally

30. symbolic representation of the basic causal-comparative design
Independent Dependent
Group Variable Variable
(E) (X) O
(C) O
Where: E (experimental group); C (control group); X (independent variable); O (dependent variable)

31. Independent Dependent
Group Variable Variable
(E) (X1) O
(C) (X2) O
Where: E (experimental group); C (control group); X (independent variable); O (dependent variable)

32. 4. Data analysis and interpretation…
…researcher uses a variety of descriptive and inferential statistics:
t-test
mean
analysis of variance
standard deviation
chi squared

33. mean
…the descriptive statistic indicating the average performance of an individual or group on a measure of some variable

34. standard deviation
…the descriptive statistic indicating the spread of a set of scores around the mean

35. t-test
…the inferential statistic indicating whether the means of two groups are significantly different from one another

36. analysis of variance (“ANOVA”)
…the inferential statistic indicating the presence of a significant difference among the means of three or more groups

37. chi squared (Χ2)
…the inferential statistic indicating that there is a greater than expected difference among group frequencies

38. Mini-Quiz… True and false…
…causal-comparative studies attempt to identify the cause-effect relationships; correlational studies do not
True

39. …causal-comparative studies typically involve two (or more) groups and one independent variable, whereas correlational studies typically involve two (or more) variables and one group
True

40. …causal-comparative studies involve relation, whereas correlational studies involve cause
False

41. …oftentimes, causal-comparative research is undertaken because the independent variable could be manipulated but should not
True

42. …one of the most important reasons for conducting causal-comparative research is to identify variables worthy of experimental investigation
True

43. …“lack of control” means that the researcher can and should manipulate the independent variable
False

44. …each group in a causal-comparative study represents a different population
True

45. …the more similar two groups are on all relevant variables except the independent variable, the stronger the study is
True

46. …there is random assignment to treatment groups from a single population in causal-comparative studies
False

47. …lack of randomization, manipulation of the independent variable, and control are all sources of weakness in a causal-comparative design
True

48. …matching, comparing homogenous groups or subgroups, and covariate analysis are strategies that enable researchers to overcome problems of initial group differences on an extraneous variable
True

49. …interpretation of the findings in a causal-comparative study requires considerable caution because the cause may be the effect and the effect may be the cause
True

50. …extraneous variables or confounding factors may be the real “cause” of both the independent and dependent variables
True

51. Fill in the blank…
…groups selected for a causal-comparative study which differ on some independent variable and comparing them on some dependent variable
comparison groups

52. …unexplained variables that influence a dependent variable
Fill in the blank…
…unexplained variables that influence a dependent variable
confounding factors
extraneous variables

53. comparing homogeneous groups
Fill in the blank…
…a method for controlling extraneous variables by comparing groups that are homogeneous with respect to the extraneous variable
comparing homogeneous groups

54. comparing homogeneous subgroups
Fill in the blank…
…a method for controlling extraneous variables by forming subgroups within each group that represent all levels of the control variable
comparing homogeneous subgroups

55. factorial analysis of variance
Fill in the blank…
…a statistical tool to determine the effects of the independent variable and the control variable on the dependent variable, both separately and in combination
factorial analysis of variance

56. analysis of covariance
Fill in the blank…
…a statistical tool to adjust initial group differences on variables
analysis of covariance

57. Fill in the blank…
…the descriptive statistic indicating the average performance of a group on a measure of some variable
mean

58. Fill in the blank…
…the descriptive statistic indicating how clustered or spread out around the mean a set of scores is
standard deviation

59. Fill in the blank…
…the inferential statistic determining whether there is a significant difference between the means of two groups
t-test

60. Fill in the blank…
…the inferential statistic determining whether there is a significant difference between the means of three or more groups
analysis of variance

61. Fill in the blank…
…the inferential statistic determining whether there is a greater than expected difference among group frequencies
chi squared

62. Fill in the blank…
…activities by which a researcher endeavors to ensure that the results of a causal-comparative study are not tainted by extraneous variables
control

63. This module has focused on...
causal-comparative studies
…which identify the cause, or reason, for existing differences in the behavior or status of groups

64. The next module will focus on...
experimental studies
...which test hypotheses to establish cause-and-effect relationships