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**Educational Research: Causal-Comparative Studies**

Richard M. Jacobs, OSA, Ph.D.

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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

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**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”)

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**Research methods... Quantitative…**

…collects and analyzes numerical data obtained from formal instruments

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**Quantitative methods... descriptive research (“survey research”)**

correlational research causal-comparative research (“ex post facto research”) experimental research

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**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

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**Research variables... Independent…**

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

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

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**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

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**Differences in causal-comparison and correlational studies…**

causal-comparative studies… …attempt to identify cause-effect relationships correlational studies… …attempt to identify relationships

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**causal-comparative studies…**

…involve two (or more) groups and one independent variable correlational studies… …typically involve two (or more) variables and one group

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**causal-comparative studies…**

…involve making comparisons correlational studies… …involve establishing relationships

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**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

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**causal-comparative studies…**

…the researcher cannot manipulate the independent variable experimental studies… …the researcher manipulates the independent variable

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**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

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**causal-comparative studies…**

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

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**Conducting a causal-comparative study…**

1. select the problem 2. select participants and instrument 3. design and procedure 4. data analysis and interpretation

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

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**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”

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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

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

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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

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**random assignment of participants to groups**

…not possible in causal-comparative studies because the groups already exist and have already received the treatment

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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

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**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

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**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

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**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

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…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

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**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

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**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)

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**Independent Dependent**

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

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**4. Data analysis and interpretation…**

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

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

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

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

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**analysis of variance (“ANOVA”)**

…the inferential statistic indicating the presence of a significant difference among the means of three or more groups

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

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**Mini-Quiz… True and false…**

…causal-comparative studies attempt to identify the cause-effect relationships; correlational studies do not True

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…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

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**…causal-comparative studies involve relation, whereas correlational studies involve cause**

False

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

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

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

False

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**…each group in a causal-comparative study represents a different population**

True

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

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

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

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…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

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…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

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

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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

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**…unexplained variables that influence a dependent variable**

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

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**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

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**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

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**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

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**analysis of covariance**

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

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

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

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

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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

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

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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

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**This module has focused on...**

causal-comparative studies …which identify the cause, or reason, for existing differences in the behavior or status of groups

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**The next module will focus on...**

experimental studies ...which test hypotheses to establish cause-and-effect relationships

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