Chapter 1 Research Strategies: How Psychologists Ask and Answer Questions

1. Chapter 1 Research Strategies: How Psychologists Ask and Answer Questions

2. Two Random Sequences • Your chances of being dealt either of these hands is precisely the same: 1 in 2,598,960.

3. Experimentation • Experiment • an investigator manipulates one or more factors (independent variables) to observe their effect on some behavior or mental process (the dependent variable) • by random assignment of participants the experiment controls other relevant factors

4. Experimentation • Double-blind Procedure • both the research participants and the research staff are ignorant (blind) about whether the research participants have received the treatment or a placebo • commonly used in drug-evaluation studies • Placebo effect • experimental results caused by expectations alone • any effect on behavior caused by administration of an inert substance or condition, which is assumed to be an active agent

5. Experimentation • Experimental Condition • the condition of an experiment that exposes participants to the treatment, that is, to one version of the independent variable • Control Condition • the condition of an experiment that contrasts with the experimental treatment • serves as a comparison for evaluating the effect of the treatment

6. Experimentation • Random Assignment • assigning participants to experimental and control conditions by chance • minimizes pre-existing differences between those assigned to the different groups

7. Experimentation • Independent Variable • the experimental factor that is manipulated • the variable whose effect is being studied • Dependent Variable • the experimental factor that may change in response to manipulations of the independent variable • in psychology it is usually a behavior or mental process

8. Experimentation

9. 100% 99 98 97 96 95 Percentage still functioning after 10 years Our Brand Brand Brand Brand X Y Z Brand of truck Statistical Reasoning

10. 100% 90 80 70 60 50 40 30 20 10 0 Percentage still functioning after 10 years Our Brand Brand Brand Brand X Y Z Brand of truck Statistical Reasoning

11. Statistical Reasoning • Mode • the most frequently occurring score in a distribution • Mean • the arithmetic average of a distribution • obtained by adding the scores and then dividing by the number of scores • Median • the middle score in a distribution • half the scores are above it and half are below it

12. 15 20 25 30 35 40 45 50 90 475 710 70 Mode Median Mean One Family Income per family in thousands of dollars Statistical Reasoning A Skewed Distribution

13. Statistical Reasoning • Range • the difference between the highest and lowest scores in a distribution • Standard Deviation • a computed measure of how much scores vary around the mean • Statistical Significance • a statistical statement of how likely it is that an obtained result occurred by chance