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

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

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

Experimentation Double-blind Procedure Placebo effect 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

Experimentation Experimental Condition Control 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

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

Experimentation Independent Variable Dependent 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

Experimentation

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

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

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

Statistical Reasoning A Skewed Distribution 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 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