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Experimental Design: Introduction

Experimental Design: Introduction. Martin, Chapter 1. Psychology as a science.

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Experimental Design: Introduction

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  1. Experimental Design: Introduction Martin, Chapter 1

  2. Psychology as a science • “Psychology is the Science of Mental Life, both of its phenomena and their conditions. The phenomena are such things as we call feelings, desires, cognitions, reasonings, decisions and the like; and, superficially considered, their variety and complexity is such as to leave a chaotic impression on the observer.” William James (1890)

  3. Methods for Investigating Hypotheses(Establishing Cause and Effect Relationships) • Correlational research • Quasi-experimental research • Experimental research Quantitative vs. Qualitative research

  4. Kinds of Variables • Independent Variables • what you manipulate • Dependent Variables • what you measure • Control Variables • what you hold constant • Random Variables • what you allow to vary randomly • Confounding variable • correlated with independent variable

  5. Correlation • Take two measures from a sample; calculate correlation coefficient • Possible questions: • is there a relationship between smoking and lung cancer? • is there a relationship between anxiety and test-taking performance? • Correlation does NOT imply causation

  6. Example of correlation

  7. Experiments • Systematically vary variables of interest • e.g., giving different drugs • Critical concepts • Variable must be manipulated by experimenter • Random assignment of participants to conditions • Avoid confounding variables

  8. Example of experiment

  9. Quasi-experimental • Separate participants based on some characteristic, e.g.: • Gender, occupation, verbal ability (VSAT) • Possible questions • Do people with high verbal ability learn new languages faster? • Accepted, but effects may be due to another factor • e.g., high-verbal people went to better high-school

  10. How to select a kind of study 1) representativeness • does this seem like the real thing? 2) control • can you manipulate something? 3) cost & effort • is it worth it to do it the painful way 4) availability • are the best kinds participants available?

  11. Randomization • Random Sampling • Choose participants randomly from the entire population • Allows generalization to population • Random Assignment • Methods for achieving random assignment • Flip coins; random numbers on arrival • Assign conditions in blocks

  12. Demo: Can you pick a random number? 1 2 3 4

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