1-2 Experiments Experiment: A controlled test of a hypothesis in which the researcher manipulates one variable to discover its effect on another. Detection of cause-and-effect relationships

Hypothesis, Participants, & Random Assignment Hypothesis: a prediction made to which the experiment tests Participants: the subject of experiments Random Assignment: assigning participants to experimental conditions, all have equal chance of being assigned to any conditions

1-5 Experimental and Control Conditions (Groups) Experimental Condition: In an experiment, a condition in which subjects are exposed to manipulations of the independent variable. Control Condition: A comparison condition in which subjects are not exposed to the same treatment as in the experimental condition.

More on Controls The Value of Controls Logic: Two groups alike in all respects (random assignment) Manipulate independent variable for one group only Resulting differences in the two groups must be due to the independent variable Extraneous variables: outside influence not part of the experiment, but which effect the outcome confounding variables: more than 1 variable which counteract the effects of other variables

Fig The basic elements of an experiment. As illustrated by the Schachter study, the logic of experimental design rests on treating the experimental and control groups exactly alike (to control for extraneous variables) except for the manipulation of the independent variable. In this way, the experimenter attempts to isolate the effects of the independent variable on the dependent variable.

1-8 Experimental Variables Independent Variable: A variable that an experimenter manipulates. Dependent Variable: A variable than an experimenter predicts will be affected by manipulations of the independent variable.

Fig Manipulation of two independent variables in an experiment. As this example shows, when two independent variables are manipulated in a single experiment, the researcher has to compare four groups of subjects (or conditions) instead of the usual two. The main advantage of this procedure is that it allows an experimenter to see whether two variables interact.

Experimental Designs: Variations Expose a single group to two different conditions Reduces extraneous variables Manipulate more than one independent variable Allows for study of interactions between variables Use more than one dependent variable Obtains a more complete picture of effect of the independent variable

1-11 Experimental Design Hypothesis: Nicotine in cigarettes impairs driving. All conditions kept the same for both groups except nicotine. Control condition is given placebo (inactive) cigarettes Number of collisions is measured.

Collecting the Results Following the completion of the experiment Data is collected Experiment is repeated to confirm results Process repeated if hypothesis is disproved Results published Experiments are of no value if kept secret Results published for benefit of psychological community

1-14 Placebo An inactive substance or fake treatment used as a control in an experiment or given by a practitioner to a patient. Serves as a control condition Practice effect: improvement from mere repletion

1-15 Experimenter Effects Unintended changes in subjects’ behavior due to cues inadvertently given by the experimenter: demand characteristics Double-Blind Study: Experiment where neither subjects nor people running the study know which subjects are in the control group and which are in the experimental group until after results are tallied. Single-Blind Study: researcher, but not participants aware

1-16 Advantages and Limitations of Experiments Experiments allow conclusions about cause-effect relationships. Participants in experiments are not always representative of larger population. Much psychology research is carried out using colleges students as participants. Field Research: Descriptive or experimental research conducted in a natural setting outside the laboratory.

Strengths and Weaknesses of Experimental Research Strengths: conclusions about cause-and-effect can be drawn Weaknesses: artificial nature of experiments ethical and practical issues