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Explore experimental & non-experimental research, basic statistics, validity, controls, and sampling methods in psychology. Learn about data analysis techniques, populations vs. samples, and strategies for controlling experiments.
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Psychology 242Research Methods II Dr. David Allbritton http://www.depaul.edu/~dallbrit
Introduction and Review • Syllabus and Course Requirements • Types of research: Experimental vs. Non-experimental • Review of Basic Statistics • Review of Validity and Control
Types of Research • Non-experimental Methods (“correlational”) • Observational research • Archival research • Case studies • Survey research • Experiments • IV & DV • Maximizes internal validity (shows causation) • Quasi-Experiments
Statistics • Sample: Descriptive Statistics • Population: Inferential Statistics
Descriptive Statistics • Measures of central tendency • Mean • Median • Mode • Measures of variability • Standard deviation (SD) • Variance (SD squared) • Correlation – measure of relatedness
Distributions • Histograms • Density Curves • Normal Distributions • Symmetrical around the mean • Mean = median = mode • Standard Deviation and area under the curve:68: 95: 99.7 rule • Example: IQ mean = 100, SD = 15
Populations and Samples • Population: all the possible scores • All living humans • All voters • Sample: a subset of the population • Random sample – best kind; unbiased • Relationship of sample mean to population mean - example
Validity & Control • Validity – is the research sound? • Threats to Validity – e.g., confounds • Control – removing threats to validity
Validity of Research • Internal Validity • Does the IV (and not some other factor) really cause the changes in the DV? • Ruling out other causes (confounds) • Construct Validity • Does the study support the theory it is supposed to and no other theories? • Ruling out other theories (alternative explanations) • External Validity • Do the results generalize to other people? • Statistical Validity • Does the IV cause the changes in the DV, or could they be due to chance?
Strategies for Control in Experiments • Subject as Own Control (within-subjects) • Random Assignment • Counterbalancing • Building in Nuisance Variables • Replication