Psychology 242 Research Methods II Dr. David Allbritton

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 - exampleexample

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