The scientific method

1. The scientific method Why psychology is a science

2. How do we know things Think of something about the world that you just know is correct Tornados never happen during the winter Cooking at home is cheaper than eating out in a restaurant It’s better to punt on 4th down and long than try to get the 1st down

3. How we know things • Sources of declarative knowledge • Authority 9/10 dentists say flossing daily prevents cavity formation Your mom tells you that you need good grades to get into college…

4. How we know things • Sources of declarative knowledge • Authority • Common sense/common knowledge Swimming immediately after eating causes cramps Playing violent video games causes violent behavior

5. How we know things • Sources of declarative knowledge • Authority • Common sense/common knowledge • Intuition Food poisoning attributed to new/novel foods Your cat ruins your stuff because he is mad at you

6. How we know things • Sources of declarative knowledge • Authority • Common sense/common knowledge • Intuition • Empiricism

7. How we know things • Sources of declarative knowledge • Authority • Common sense/common knowledge • Intuition • Empiricism Not mutually exclusive

8. What is empiricism? • Knowledge must be grounded in observations • These observations are gathered through the use of the scientific method Set of techniques that allow for the evaluation of ideas based on evidence

9. What is empiricism? • Knowledge must be grounded in observations • These observations are gathered through the use of the scientific method

10. Application of the scientific method Share findings Generate theory Interpret results Articulate hypothesis analytical theoretical Gather data Design study Make prediction experimental

11. The scientific method Share findings Generate theory Interpret results Articulate hypothesis theoretical Gather data Design study Make prediction

12. Theories, hypotheses, and predictions • Main components of the scientific method • Theory: a model that potentially explains a set of observations/phenomena • Does NOT mean that the explanation is lacking evidence • Has different meanings in science compared to everyday language The ‘theory’ of evolution The ‘theory’ of gravity

13. Theories, hypotheses, and predictions • Main components of the scientific method • Theory: a model that potentially explains a set of observations/phenomena • Does NOT mean that the explanation is lacking evidence • Has different meanings in science compared to everyday language The ‘theory’ of gravity

14. Theories, hypotheses, and predictions • Main components of the scientific method • Theory: a model that potentially explains a set of observations/phenomena The burning sensation on your tongue after eating spicy foods is caused by chemicals in the peppers that bind to your taste buds

15. Theories, hypotheses, and predictions • Main components of the scientific method • Theory: a model that potentially explains a set of observations/phenomena • Hypothesis: idea about how the world operates that follows directly from a theory • Suggests some systematic, predictable pattern between phenomena Ingesting foods that cause these chemicals to ‘let go’ of your taste buds will soothe the burning feeling on your tongue

16. Theories, hypotheses, and predictions • Main components of the scientific method • Theory: a model that potentially explains a set of observations/phenomena • Hypothesis: idea about how the world operates that follows directly from a theory • Prediction: forecast of how data will come out in a particular study • Specific only to the study in question, not generalized to other situations

17. Theories, hypotheses, and predictions • Main components of the scientific method • Theory: a model that potentially explains a set of observations/phenomena • Does NOT mean that the explanation is lacking evidence • Has different meanings in science compared to everyday language • Hypothesis: idea about how the world operates that follows directly from a theory • Suggests some systematic, predictable pattern between phenomena • Prediction: forecast of how data will come out in a particular study • Specific only to the study in question, not generalized to other situations general specific

18. Theories, hypotheses, and predictions • Parental Investment Theory • Theory: The sex with smaller obligate parental investment will compete for access to the sex with larger obligate investment Trivers, 1972

19. Theories, hypotheses, and predictions • Parental Investment Theory • Theory: The sex with smaller obligate parental investment will compete for access to the sex with larger obligate investment Trivers, 1972

20. Theories, hypotheses, and predictions • Parental Investment Theory • Theory: The sex with smaller obligate parental investment will compete for access to the sex with larger obligate investment • Hypothesis: The higher investing sex will be more selective in choosing mating partners than the lower investing sex • Prediction: men will be more likely to agree to sleep with a stranger than will women “Will you go out on a date with me tonight?” “Will you go to bed with me tonight?” Trivers, 1972 Clark & Hatfield, 1986 “Will you go out on a date with me tonight?”

21. Theories, hypotheses, and predictions Go on a date tonight Go to bed with me tonight Women Men

22. Theories, hypotheses, and predictions • The most important property of theories, hypotheses, and predictions is that they are falsifiable • Must be some data that can disconfirm prediction ✖ ✔ Get better Die Die Too far gone for treatment

23. Theories, hypotheses, and predictions • The most important property of theories, hypotheses, and predictions is that they are falsifiable • Must be some data that can disconfirm prediction ✖ ✔ Don’t get what you imagine Get what you imagine Don’t get what you imagine Didn’t believe hard enough

24. The scientific method Share findings Generate theory Interpret results Articulate hypothesis Gather data Design study Make prediction experimental

25. Testing predictions • Need tools to measure the dimensions that are of interest Imagine you are testing the hypothesis that stronger people are quicker to anger than weaker people How would you measure strength? How would you measure anger?

26. Testing predictions • Need tools to measure the dimensions that are of interest • Require operational definitions – concrete, measureable descriptions of the dimensions of interest in a study • Good operational definitions: • do not rely on subjective judgments • make it easy for others to exactly replicate • have high reliability • have high construct validity Reliability Construct validity Does a measure produce the same results when repeated under the same conditions? Does a measure actually measure the dimension you want it to? “consistency” “accuracy”

27. Reliability vs. validity Operational definitions Could be survey, physiological measurement, reaction time task, etc

28. Reliability vs. validity Operational definitions ☐ validity ✗ ☐ reliability ✓ Thurs Fri Mon Tues Weds 221 219 220 221 222 240 lbs. (actual weight) average = 220.6

29. Reliability vs. validity Operational definitions ☐ validity ✓ ☐ reliability ✗ Thurs Fri Mon Tues Weds 230 241 231 248 254 240 lbs. (actual weight) average = 240.8

30. Reliability vs. validity Operational definitions ☐ validity ✓ ☐ reliability ✓ Thurs Fri Mon Tues Weds 240 241 241 240 239 240 lbs. (actual weight) average = 240.2

31. Next time… • Research designs