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© 2011 Pearson Education, Inc. All rights reserved. 2 The (Never-Ending) Search for Causation Establishing causation among variables : »Produces increased understanding of those variables »Results in the ability to manipulate conditions in order to produce desired changes

© 2011 Pearson Education, Inc. All rights reserved. 3 Experimental Research Can demonstrate cause-and-effect very convincingly Very stringent research design requirements Experimental design requires: »Randomly selected participants who are randomly assigned to groups (experimental and control) »Independent treatment variable that can be applied to the experimental group »Dependent variable that can be measured in all groups

© 2011 Pearson Education, Inc. All rights reserved. 4 Quasi-Experimental Research Used in place of experimental research when random assignment to groups is not feasible Otherwise, very similar to true experimental research

© 2011 Pearson Education, Inc. All rights reserved. 5 Fundamentals of Experimental and Quasi-Experimental Research Cause and effect: »Incorporates a temporal element—the cause is a condition that exists prior to the effect; effect is a condition that occurs after the cause »There exists a “logical connection”—cause-and-effect is demonstrated when manipulation of the independent variable results in differences in the dependent variable (as evidenced by comparing the experimental group to the control group)

© 2011 Pearson Education, Inc. All rights reserved. 6 Fundamentals of Experimental and Quasi-Experimental Research (cont’d.) Random selection and random assignment : »Distinguish between “selection” and “assignment” »Both help to ensure that groups are equivalent and to control for extraneous variables »If you incorporate random selection and random assignmentExperimental research »If you incorporate random selection but not random assignment Quasi-experimental research

© 2011 Pearson Education, Inc. All rights reserved. 7 Fundamentals of Experimental and Quasi-Experimental Research (cont’d.) When to use experimental research design : »If you strongly suspect a cause-and-effect relationship exists between two conditions, and »At least randomly assigned group is available to participate, and »The independent variable can be introduced to participants and can be manipulated, and »The resulting dependent variable can be measured for all participants

© 2011 Pearson Education, Inc. All rights reserved. 8 Fundamentals of Experimental and Quasi-Experimental Research (cont’d.) Commonly used experimental design notation : X 1 =treatment group X 2 =control/comparison group O=observation (pretest, posttest, etc.) R=random assignment

© 2011 Pearson Education, Inc. All rights reserved. Common Experimental Designs Single-group pretest-treatment-posttest design : 9 OXOOXO »Technically, a pre-experimental design (only one group; therefore, no random assignment exists) »Overall, a weak design—no control group (for comparison purposes); pretest sensitization; experimenter effects (therefore, cannot be sure about conclusions)

© 2011 Pearson Education, Inc. All rights reserved. 10 Common Experimental Designs (cont’d.) Two-group treatment-posttest-only design : RX1ORX2ORX1ORX2O »Here, we have random assignment to experimental, control groups »A better design, but still weak—cannot be sure that groups were equivalent to begin with

© 2011 Pearson Education, Inc. All rights reserved. 11 Common Experimental Designs (cont’d.) Two-group pretest-treatment-posttest design : ROX1OROX2OROX1OROX2O »A substantially improved design—previously identified errors have been reduced

© 2011 Pearson Education, Inc. All rights reserved. 12 Common Experimental Designs (cont’d.) Solomon four-group design : ROX1OROX2ORX1ORX2OROX1OROX2ORX1ORX2O »A much improved design—how?? »One serious drawback—requires twice as many participants

© 2011 Pearson Education, Inc. All rights reserved. 13 Common Experimental Designs (cont’d.) Factorial designs : ROX1OROX2 OROX1 OROX2 OROX1OROX2 OROX1 OROX2 O »Incorporates two or more factors »Enables researcher to detect differential differences (effects apparent only on certain combinations of levels of independent variables)

© 2011 Pearson Education, Inc. All rights reserved. 14 Common Quasi-Experimental Designs Posttest-only design with nonequivalent groups : X1OX2OX1OX2O »Uses two groups from same population »Questions must be addressed regarding equivalency of groups prior to introduction of treatment

© 2011 Pearson Education, Inc. All rights reserved. 15 Common Quasi-Experimental Designs (cont’d.) Pretest-posttest design with nonequivalent groups : OX1OOX2OOX1OOX2O »A stronger design—pretest may be used to establish group equivalency

© 2011 Pearson Education, Inc. All rights reserved. 16 Common Quasi-Experimental Designs (cont’d.) Time series designs : O O O O X O O O O »Uses a single group of participants »Examines possible changes over time

© 2011 Pearson Education, Inc. All rights reserved. 17 Similarities Between Experimental and Quasi-Experimental Research Cause-and-effect relationship is hypothesized Participants are randomly selected and randomly assigned (experimental) or randomly selected and nonrandomly assigned (quasi-experimental) Application of an experimental treatment by researcher Following the treatment, all participants are measured on the dependent variable Data are usually quantitative (exception is single- subject designs); analyzed by looking for significant differences on the dependent variable

© 2011 Pearson Education, Inc. All rights reserved. 18 Single-Subject Designs Similar to experimental and/or quasi-experimental designs (i.e., essentially having a pretest, an intervention, and a posttest), but with only one participant Basic single-subject design: »Purpose is to monitor effects on one subject »Results can be generalized only with great caution O O O | X O X O | O O O

© 2011 Pearson Education, Inc. All rights reserved. 19 Variations of the basic single-subject design include: » AB design » ABA design (a.k.a. “ reversal design ”) » Alternating treatment design » Multiple baseline design Single-Subject Designs (cont’d.)

© 2011 Pearson Education, Inc. All rights reserved. 20 Internal and External Validity “Validity of research” refers to the degree to which the conclusions are accurate and generalizable Both experimental and quasi-experimental research are subject to threats to validity If threats are not controlled for, they may introduce error into the study, which will lead to misleading conclusions

© 2011 Pearson Education, Inc. All rights reserved. 21 Threats to Internal Validity Internal validity —extent to which differences on the dependent variable are a direct result of the manipulation of the independent variable » Differential selection of participants —participants are not selected/assigned randomly » History —when factors other than treatment can exert influence over the results; problematic over time » Maturation —when changes occur in dependent variable that may be due to natural developmental changes; problematic over time

© 2011 Pearson Education, Inc. All rights reserved. 22 Threats to Internal Validity (cont’d.) » Testing —also known as “pretest sensitization”; pretest may give clues to treatment or posttest and may result in improved posttest scores » Attrition (mortality) —loss of participants

© 2011 Pearson Education, Inc. All rights reserved. 23 Threats to External Validity External validity —extent to which the results can be generalized to other groups or settings » Population validity —degree of similarity among sample used, population from which it came, and target population » Personological variables —application of findings based on individual differences » Ecological validity —physical or emotional situation or setting that may have been unique to the experiment

© 2011 Pearson Education, Inc. All rights reserved. 24 “The Influence of Computer-Assisted Instruction on Eighth Grade Mathematics Achievement” Published Example of Quasi- Experimental Research

© 2011 Pearson Education, Inc. All rights reserved. 25 “A Language Programme to Increase the Verbal Production of a Child Dually Diagnosed with Down Syndrome and Autism” Published Example of Single-Subject Research

© 2011 Pearson Education, Inc. All rights reserved. 26 Applying Technology… Web sites related to experimental and quasi- experimental research Dr. Trochim’s discussion of "Experimental Designs" (socialresearchmethods.net/kb/desexper.htm)socialresearchmethods.net/kb/desexper.htm Dr. Trochim’s discussion of "Two-Group Experimental Designs" (socialresearchmethods.net/kb/expsimp.htm)socialresearchmethods.net/kb/expsimp.htm Dr. Trochim’s discussion of "Factorial Designs" (socialresearchmethods.net/kb/expfact.htm)socialresearchmethods.net/kb/expfact.htm Dr. Trochim’s discussion of "Randomized Block Designs" (socialresearchmethods.net/kb/expblock.htm)socialresearchmethods.net/kb/expblock.htm Dr. Trochim’s discussion of "Covariance Designs" (socialresearchmethods.net/kb/expcov.htm)socialresearchmethods.net/kb/expcov.htm

© 2011 Pearson Education, Inc. All rights reserved. Dr. Trochim’s discussion of "Hybrid Experimental Designs" (socialresearchmethods.net/kb/exphybrd.htm)socialresearchmethods.net/kb/exphybrd.htm Dr. Trochim’s examination of quasi-experimentation (socialresearchmethods.net/kb/quasiexp.htm)socialresearchmethods.net/kb/quasiexp.htm Dr. Trochim’s discussion of "The Nonequivalent Control Group Design" (socialresearchmethods.net/kb/quasnegd.htm)socialresearchmethods.net/kb/quasnegd.htm Dr. Trochim’s discussion of "Other Quasi-Experimental Designs" (socialresearchmethods.net/kb/quasioth.htm)socialresearchmethods.net/kb/quasioth.htm 27 Applying Technology… More web sites related to experimental and quasi- experimental research