PS Research Methods I with Kimberly Maring Unit 9 – Experimental Research Chapter 6 of our text: Zechmeister, J. S., Zechmeister, E. B., & Shaughnessy, J. J. (2001). Essentials of research methods in Psychology. New York, NY: McGraw-Hill

Four Goals of Research in Psychology Description Prediction Understanding Creating change

Psychological Researchers Use Observation Surveys Psychological Researchers Make Predictions from Information Gathered Above In Which They Discover How These Measures and Observations Covary (Correlations)

In this chapter, we will discuss different types of experimental research designs. We will examine the underlying logic of experimental research and the procedures for comparing different conditions in experimental designs. We will also address issues of internal and external validity of experiments, as well as the ways in which data from experimental designs are analyzed. (Zechmeister, Zechmeister, & Shaughnessy, 2001, p. 146)

Learning Objectives – Understand the logic of experimental designs – Identify the types of experimental designs – Evaluate internal and external validity issues – Understand basic concepts in analyzing data

Experimental Research Independent variables – factors researcher controls/manipulates Dependent variables – measures used to observe effect (if any) of the independent variables The Logic behind well-designed experiments– the only factor left to vary is the Independent variable

Experimental Research In a true experiment the researcher manipulates one or more factors and measures An experiment has internal validity when we are able to state confidently that the independent variable caused differences between groups on the dependent variable.True experiments are founded on random assignment

Control and Internal Validity Internal validity – An experiment has internal validity when we are able to state confidently that the independent variable caused differences between groups on the dependent variable.

Research Designs Independent Groups Designs – separate groups participate in the different independent variable conditions – Random Groups Design With Random Assignment every participant has an equal chance of being assigned to either group

Research Designs Independent Groups Designs – Matched Groups Design – the researcher makes the groups equivalent by matching participants in the different conditions using a pretest or matching task

Research Designs Independent Groups Designs – Matched Groups – Natural Groups Design – individual difference variables/participant variables Independent variable with selected levels of an individual differences variable

Research Designs Repeated Measures Design or Within-Subjects Design – Participants participate in each condition of the experiment – Each participant asks as his/her own “control” – Counterbalancing – order of conditions is “counterbalanced” to avoid practice effects Each condition of the experiment must appear in each ordinal position )(i.e., first, second, third) equally often

External Validity Extent to which findings from an experiment can be generalized to individuals, settings, and conditions beyond the scope of the specific experiment Replication – repeating experiment with different samples, populations, setting, to search for “robust” research findings

Analysis of Experimental Designs Check the data – – Frequency Distributions Outliers Summarize the data – – Descriptive Statistics Venus reflected on the Sea of Cortez

Analysis of Experimental Designs Confirm what the data reveal – Inferential Statistics – test whether differences between group means can be attributed to the effect of the IV, not to chance factors – Confidence Intervals – gives us information about the possible range of values we can expect for the population characteristic

Analysis of Experimental Designs Null Hypothesis Testing – Researchers begin by assuming no effect = “Null Hypothesis” – How likely is the difference between sample means observed in our experiment, assuming there is no difference between the population means – ANOVA, F, t

Analysis of Experimental Designs Null Hypothesis Testing – Statistical significance = indicates the difference between observed means in the experiment is larger than would be expected by chance if the null hypothesis is true – Type I Error – rejecting the Null Hypothesis when it is true – Type II Error – fails to reject the Null Hypothesis when it is false

Thinking Critically About Experimental Research Intact groups Extraneous variables Subject loss Expectations – Demand characteristics – Placebo – Experimenter Effects – Double-blind procedures

Venus reflected on the Sea of Cortez

Final Paper Student provides a detailed description of the experimental method which they felt was most appropriate to use [a repeated measures design, or one of the independent group designs]. A thorough justification of the selected method is provided, along with appropriate references to the text or other outside sources. 35 points

Final Paper A clear identification of the target population is provided, along with a detailed description and justification of a sampling plan. Appropriate references to the text are provided. 25 points

Final Paper Ethical issues that may be involved with the study are clearly described here, along with ways to avoid these issues and/or address them as per APA guidelines. 25 points

Final Paper Potential threats to both the internal and external validity of the study are clearly described, and the student is able to consider ways to work around this in the future. Appropriate references to the text are made. 35 points

Final Paper Possible results of this study are described, and any limitations to the conclusions are addressed. 25 points

Final Paper Reflects ability to utilize concepts in personal and professional settings. 20 points

Final Paper Structure: Includes introduction with clear thesis statement, complete paragraphs, and brief summary paragraph rephrasing thesis. 20 points

Final Paper Mechanics: Uses correct grammar, spelling, punctuation, and APA format. Free of typographical errors. Meets the length requirement (not including the cover page or reference page). 15 points