Understanding Research Methods in Psychology: From Reasoning Fallacies to Normal Distributions

1. Research Methods Chapter 2

2. Reasoning Fallacies • Hindsight bias – tendency to believe, after learning an outcome, that we would have foreseen it • The “I knew it all along” phenomenon

3. Psychology as Science • Empiricism – belief that accurate knowledge of the world requires observation of it • Limitations of casual observation: • Unstable • Can’t tell us about the properties we might be interested in

4. Psychology as a Science -cont- • So we must use measurement to: • Define the property we want to measure in concrete terms • Operational definition – description of procedures used to define research variables • Ex: human intelligence may be operationally defined as what an intelligence test measures

5. Psychology as a Science -cont- • A good measurement has • Validity – allows one to draw accurate inferences from it • Replication– produces the same result whenever it is used to measure the same thing

6. Case study • Studying a single individual in depth

7. Naturalistic observation • Unobtrusively observing people in their natural environment • Avoid demand characteristics – aspects that cause people to behave as they think an observer wants/expects them to behave • Limitations: • Some things psychologists want to observe don’t occur naturally • Some things can only be gathered from direct observation with a person

8. Survey • Survey - uses a representative sample of people to estimate attitudes or reported behaviors of a whole population • Limitation: • Respondents may not answer honestly

9. Survey -cont- • Population - all the cases in a group being studied from which samples may be drawn • Random sample - every member of a population has an equal chance of inclusion

10. Correlational Studies • Correlation – the “co-relationship” or pattern of co-variation between two variables • Positive – two sets of variables go up or down together • Negative – two sets of variables relate inversely

11. Correlation vs. Causation • Third-variable correlation – two variables may be correlated only because they are both caused by a third variable • Correlation does not prove causation

12. Correlation -cont- • Illusory correlation: The perception of a relationship where none exists

13. Experimentation • Used to establish the casual relationship between variables • Independent variable – variable that is manipulated • Is “independent” of what the participant says/does • Dependent variable – variable that is measured • “Depends” on what the participant says or does • Control group – group that does not receive the treatment • Experimental group – group does receive the treatment

14. Experimentation -cont- • An experiment is internally valid when: • An independent variable has been effectively manipulated • A dependent variable has been measured in an unbiased way with a valid, powerful, and reliable measure • A correlation has been observed between the independent and the dependent variable • External validity – property of an experiment in which the IV and DV is operationally defined in a normal, typical, or realistic way

15. Experimentation -cont- • It is generally not feasible to use a random sample when conducting an experiment • Experiments utilize • Random assignment - assigning participants to experimental and control groups by chance • Double blind procedure - neither the research participants nor the research staff know if participants received the treatment or a placebo - sugar pill • Eliminates placebo effect - experimental results caused by expectations alone

16. Measures of Central Tendency • Mean – sum of a set of scores in a distribution divided by the number of scores • Extreme scores have a greater impact on the mean than on the mode or median • Median – score that divides a frequency distribution exactly in half, so that the same number of scores lie on each side of it • Mode – the most frequently occurring score in a distribution

17. Measures of Variation • Definition – a single score that presents information about the spread of scores in a distribution • Range – the highest score in a distribution minus the lowest score • Standard deviation – a standard measurement of how much the scores in a distribution deviate from the mean

18. Normal distribution • Form a bell-shaped curve • In a normal distribution of test scores, 50% of scores fall at or above the mean score and 50% of scores fall at or below the mean score • Approximately 1/3 of the scores fall one standard deviation below the mean and 1/3 fall one standard deviation above the mean

19. All score-based normal curves have the following 68-95-99.7 rule in common: • Approximately 68% of all scores fall within one standard deviation of the mean • Approximately 95% fall within two standard deviations of the mean • Approximately 99.7% fall within three standard deviations of the mean

20. Skewed distributions • Positively skewed distributions have more scores on the low end of the scale • The median is the best representation of central tendency • Negatively skewed distributions have more scores on the high end of the scale • The median is a better representative of central tendency

22. Ethics • Obtain informed consent – written agreement to participate in a study made by an adult who has been informed of all the risks participation may entail • Participation may not be coerced • Psychologists must protect participants from physical or psychological harm • Risk of embarrassment or minor pain must be outweighed by social benefits of new knowledge gained by study • Must provide a debriefing – verbal description of true nature and purpose of study