Causal (1)

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Educational Research:Causal-Comparative Studies

EDU 8603

Educational Research

Richard M. Jacobs, OSA, Ph.D.

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Research...

The systematic application of afamily of methods employed toprovide trustworthy informationabout problems…an ongoing process based on many

accumulated understandings andexplanations that, when taken togetherlead to generalizations about problemsand the development of theories

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The basic steps of research...

Scientific and disciplined inquiry is anorderly process, involving:

description and execution of

procedures to collection information(“method ”) objective data analysis

statement of findings (“ results ”)

recognition and

identification of atopic to be studied (“ problem ”)

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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 researchcausal-comparative research (“ex p os t fac to research”)

experimental research

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causal- comparative research (“ ex p os tfacto research”)…at least two different groups are

compared on a dependent variable or measure of performance (called

the “effect”) because theindependent variable (called the“cause”) has already occurred or

cannot be manipulated

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dependent variable …

…the change or difference occurringas a result of the independentvariable

…(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, orreason, for pre-existing differences ingroups of individuals

…called an “ ex p os t fac to ” studybecause both the effect and thealleged cause have already occurredand must be studied in retrospect

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Differences in causal-comparisonand correlational studies…

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

relationshipscorrelational studies… …attempt to identify relationships

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Differences in causal-comparisonand experimental studies…

causal- comparative studies… …individuals are not randomly selected but

selected because they belong to groupsexperimental 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 variableexperimental studies… …the researcher manipulates the

independent variable

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causal- comparative studies… …the independent variable has already

occurred and cannot be manipulatedexperimental studies… …the researcher manipulates the

independent variable to determine itseffects

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causal- comparative studies… …the random sample is selected from two

already-existing populationsexperimental studies… …the random sample is selected from a

single population

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Conducting a causal-comparativestudy…

1. select the problem

2. select participants and instrument3. design and procedure4. data analysis and interpretation

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1. select the problem…

…the researcher starts with an effectand 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 oftheir respective populations andsimilar with respect to critical

variables other than the independentvariable…called “ comparison groups ”

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3. design and procedure…

…the performance of the groups iscompared using some validdependent variable measure

(“ instrument ”) …lack of randomization, manipulation,and control are sources of weakness

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control

…the process by which the researcherattempts to ensure that the findingsare as free of researcher bias anderror 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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pair-wise matching

…f i r s t : find a participant in the second (third,fourth, etc.) group with the same or similarscore on the control (nonmanipulated)variable as the participant in the first group

…seco n d : if a participant in either groupdoes not have a suitable match, theparticipant is eliminated from the study

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comparing homogeneous groups

…control for extraneous variables thatare homogeneous with respect to theextraneous variables

…l imi ta t ion : lowers the number ofparticipants in the study and, ofcourse, limits the generalizability ofthe 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 permitsthe researcher to determine whether theindependent variable affects thedependent variable differently at differentlevels 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 independentand control (nonmanipulated) variable onthe dependent variable, both separatelyand in combination

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…FANOVA allows the researcher to

determine if there is an interactionbetween the independent variableand the dependent variable such thatthe independent variable operatesdifferently at different levels of theindependent variable building it intothe research design

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analysis of covariance (“ANCOVA”) …statistically adjusts initial group

differences on a dependent variable forinitial differences on some other variablerelated to performance on the dependentvariable

…removes initial differences so that theresults can be fairly compared as if the twogroups started equally

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symbolic representation of the basiccausal-comparative design

Independent DependentGroup 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 DependentGroup Variable Variable

(E) (X 1) O(C) (X 2) 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 ofdescr ip t ive and inferent ia l s tat is t ics :

mean

standarddeviation

t-test

analysis ofvariancechi squared

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mean

…the descriptive statistic indicating theaverage performance of an individualor group on a measure of somevariable

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standard deviation

…the descriptive statistic indicating thespread of a set of scores around themean

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t-test

…the inferential statistic indicatingwhether the means of tw o groups aresignificantly different from oneanother

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analysis of variance (“ANOVA”)

…the inferential statistic indicating thepresence of a significant differenceamong the means of th ree or m oreg r o u p s

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chi squared ( Χ 2 )

…the inferential statistic indicating thatthere is a greater than expecteddifference among group frequencies

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…causal -comparative studies typicallyinvolve two (or more) groups and oneindependent variable, whereascorrelational studies typically involvetwo (or more) variables and one group

True

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…causal -comparative studies involverelation, whereas correlationalstudies involve cause

False

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…oftentimes, causal -comparativeresearch is undertaken because theindependent variable could bemanipulated but should not

True

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…one of the most important reasonsfor conducting causal-comparativeresearch is to identify variablesworthy of experimental investigation

True

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…“lack of control” means that theresearcher can and shouldmanipulate the independent variable

False

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…each group in a causal -comparativestudy represents a differentpopulation

True

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…there is random assignment totreatment groups from a singlepopulation in causal-comparativestudies

False

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…matching, comparing homogenousgroups or subgroups, and covariateanalysis are strategies that enableresearchers to overcome problemsof initial group differences on an

extraneous variableTrue

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…extraneous variables or confoundingfactors may be the real “cause” ofboth the independent and dependentvariables

True

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Fill in the blank…

…groups selected for a causal -comparative study which differ onsome independent variable and

comparing them on some dependentvariablecomparison groups

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…unexplained variables that influencea dependent variable

confounding factors

extraneous variables

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…a method for controlling extraneousvariables by comparing groups thatare homogeneous with respect to

the extraneous variablecomparing homogeneous groups

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…a method for controlling extraneousvariables by forming subgroupswithin each group that represent alllevels of the control variable

comparing homogeneous subgroups

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…a statistical tool to adjust initialgroup differences on variables

analysis of covariance

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…the descriptive statistic indicatingthe average performance of a groupon a measure of some variable

mean

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…the descriptive statistic indicatinghow clustered or spread out aroundthe mean a set of scores is

standard deviation

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…the inferential statistic determiningwhether there is a significantdifference between the means of tw o groups

t-test

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…activities by which a researcherendeavors to ensure that the resultsof a causal-comparative study arenot tainted by extraneous variables

control

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This module has focused on...

…which identify the cause, orreason, for existing differences inthe behavior or status of groups

causal-comparative studies

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Causal (1)

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