Psychology and the scientific method

1. Psychology and the scientific method • Importance of scientific method • Historical importance (last 1000 years) • Importance for psychology (SCIENCE of behavior and subjective experience

2. Overview of Scientific method

3. Data gathering is critical • Gather evidence –data, data, data • Critical step • What happens if evidence gathered incorrectly • Main data gathering methods • Descriptive vs. experimental • Major differences • Advantages and disadvantages

4. Gathering data – descriptive research • First step, describe phenomenon • Importance of complete and accurate description • Operational definitions • Ways of gathering descriptive data • Naturalistic observations • Advantages • Disadvantages • Potential concerns • Observer reactivity

5. Naturalistic observation of nonhumans

6. Naturalistic observation of humans

7. Example of naturalistic study • Rhesus monkeys have even ratio of males to females at birth • By adolescence many more females than males • Why do males die • Use naturalistic study to examine this

9. Descriptive techniques (cont’d) • Case studies – Used often in Neuropsychology • Relatively rare in other areas • Advantages • HM and short term memory • Disadvantages • Potential concerns • Representativeness of the case • Interviews/surveys • Advantages • Disadvantages • Potential concerns • Biased samples

10. Bias sampling in 1948 presidential election

11. Correlational research • Examines relationship between two or more variables • Smoking and lung cancer • Are people who smoke more, more likely to get lung cancer? • Exercise and heart disease • Does increased exercise lead to reduced heart disease? • Still descriptive because we don’t manipulate anything • However, does allow for prediction

12. Measures of correlation • Measures how strong relationship is between variables • Correlation coefficient (r) • Range • Between +1 and -1 • Direction • Positive indicates variables move in same direction • Negative indicates variables move in opposite direction • Strength • Closer to +1/-1 stronger relationship • 0 correlation means no relationship between variables

13. Some common POSITIVE correlations One more SAT and GPA < 0.2

14. Correlation and Causation • Correlation between two variables DOES NOT (again DOES NOT) mean that one variable CAUSED a change in the other • Correlation between height and weight DOES NOT mean that “tallness” causes heaviness • Negative correlation between smoking and lifespan DOES not mean that increased smoking causes lower lifespan.

15. Correlation and Causation (cont’d) • Why correlation cannot be used to infer causation • Third variable problem • Correlation between number of churches in a city and number of murders in a city about +0.8 • Correlation between height and hair length about –0.8 • Why is this the tobacco industry’s favorite scientific principle? • Direction of correlation

16. Selecting appropriate method • True “art” of the researcher • Separates good from best • Weigh relative advantages and disadvantages • What are you willing to live with • What are you not willing to sacrifice • Examples • What year of college are students most sexually active? • Hypotheses? • Methods • Direct observation?? • – NO! • Interview/survey • Advantages and disadvantages • Do we use?