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FDN 5000 Research in Education
Dr. George H. Olson, Instructor
Research DesignsDescriptive Research DesignsCorrelation Research DesignsCausal-comparative DesignsExperimental DesignsNon-experimental Designs
Single-subject designs
Purposes of Research Designs
Provide guidance in conducting researchProvide guidance in interpreting research
Guidance in recognizing types of research Guidance in recognizing potential threats to
the validity of research conclusionsHelp guard against threats to internal and
external validity
Descriptive research designs
Survey research Longitudinal research designs
Cohort designsQuasi-cohort designs
Cross-sectional researchCase studiesEthnographic studies
Correlational research designs
Objective: study the relationship between variables Examine scatter plots (e.g., pages 223
and 225 in our text) Compute correlation coefficients
range from -1 through 0 to +1do not imply causationlack of correlation does NOT imply no
causation
Interpreting correlations
Rules of thumb:Correlation coefficient Strength of relationship
.00 to .20 negligible .24 to .40 low .40 to .60 moderate .60 to .80 substantial .80 to 1.00 high, very high
Causal comparative research designs
A.k.a. ex-post-facto designsAimed at discovering cause and effect
relationshipsDefined groups are compared after
they have been formedTheory plays an important role
In arguing for the cause-effect relationship In eliminating rival explanations
Causal comparative designs: An example
Of students receiving the This proportion is known to
following grades…. drive a car to school
A 8%B 23%C 43%D 77%F 96%
What should the superintendent conclude?
Diagramming Experimental Research Designs
Symbols used: T = treatment intervention C = control or comparison condition
(often simply no treatment) O = observation (often some test score) R = designates random assignment M = designates matching
Examples of Research Design Diagrams
(1) T O
(2) O1 T O2
O1 T O2
(3) ----------------------- (No Random Assignment)
O1 C O2
Three pre-experimental designs
Three designs frequently used in education research that… are not sufficient for permitting strong
tests of causal hypotheses often due suggest new ideas
One-group posttest-only designOne-group pretest-posttest designComparison-group posttest-only design
One-group, posttest-only research design
T O
A treatment followed by an observation Should not be confused with the one-shot case
study Threats to internal validity:
ALL (except regression and mortality) Threats to external validity:
ALL
One-group pretest-posttest research design
Opre T Opost
One of the most frequently used research
designs in education Threats to internal validity:
extraneous events (history and maturation) statistical regression testing experimenter and subject effects
Threats to external validity selection and settings interactions with treatment
Comparison-group, posttest-only design
T O--------------C O--------------C2 O--------------C3 O
Comparison-group, posttest-only design
Threats to internal validity Since the comparison groups are non-
equivalent, the major threat is selection Other threats include mortality, and
subject and experimenter reactive effectsThreats to external validity
Selection and settings by treatment interaction
True experiment research designs
Randomized experimentsResult in probabilistic equivalenceNot a panacea that rules out all
threats to internal validity Does not control for experimenter and
subject reactive effects. Does not guarantee group equivalency
(especially in small samples).
Randomized posttest comparison group design
T OR: ---------------
C O
Note: R: means RANDOMIZATION
Randomized pretest-posttest control group design
Opre T Opost
R: ---------------------------Opre C Opost
R: ---------------------------Opre C2 Opost
Randomized matched-group design
T OM: R: ---------------
C O
Randomized factorial designs
TA1,B1 O---------------TA1,B2 O
R: ---------------TA2,B1 O---------------TA2,B2 O
Factorial Design: Example
Method (B)____ Word Type (A) Computer Handwriting
B1 B2
Easy A1 20 26Hard A2 16 20
____________________________
Quasi-experiments: Time series designs
O1 O2 O3 O4 T O5 O6 O7 O8
Pre-observations to establish a baseline
A treatment intervention Post-observations to establish new
baseline
Quasi-experiments: Non-equivalent control groups
In these designs, randomization is either not possible or not feasible.
Characterized by ... using intact groups for treatment and
comparison manipulated independent variable
Often, the best we can expect from education research
Non-equivalent, control group, pretest-posttest design
Opre T Opost
------------------------- Opre C Opost
Except for reactive effects, most threats to internal validity are controlled
Again settings and selection by treatment interactions pose threats to external validity
Matched comparison group, posttest design
T OM: ---------
C OValidity depends upon how well
matching is achievedPotential threats to internal validity
are same as those for posttest-only designs
Single-subject designs
Similar to time-series designs, only with a single individual
Repeated measurements over time (baselines)
Subjects serve as their own controlsInvolve a manipulated independent
variable (the intervention)
Basic single-subject designs
Reversal: A - B - ADouble reversal: A - B - A - BMultiple baseline:
A - B - A------------------------ A - B - A------------------------
A - B - A------------------------
A - B - AA is a period of no treatmentB is a period of treatment
Example of a stable baseline
0 10 20 30 40 50 60 70 80 90
100
Stable Baseline Pattern
Example of an increasing baseline
0
20
40
60
80
100
Increasing Baseline Pattern
Non-experimental research designs
Characterized by the lack of manipulation of an independent variable
Three types of non-experimental research designs: Causal comparative research designs Correlational research designs Descriptive research designs