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Transcript of 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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Fill in the blank…
…unexplained variables that influencea dependent variable
confounding factors
extraneous variables
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Fill in the blank…
…a method for controlling extraneousvariables by comparing groups thatare homogeneous with respect to
the extraneous variablecomparing homogeneous groups
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Fill in the blank…
…a method for controlling extraneousvariables by forming subgroupswithin each group that represent alllevels of the control variable
comparing homogeneous subgroups
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Fill in the blank…
…a statistical tool to adjust initialgroup differences on variables
analysis of covariance
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Fill in the blank…
…the descriptive statistic indicatingthe average performance of a groupon a measure of some variable
mean
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Fill in the blank…
…the descriptive statistic indicatinghow clustered or spread out aroundthe mean a set of scores is
standard deviation
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Fill in the blank…
…the inferential statistic determiningwhether there is a significantdifference between the means of tw o groups
t-test
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Fill in the blank…
…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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