Random assignment—division of the sample into groups so that every individual has
an equal chance of being put in any group or condition.Confounding variables—factors that cause differences between the experimental group
and the control group other than the independent variable.Operational definition—a description of the specific procedure used to determine the
presence of a variable.Experimenter bias—a phenomenon that occurs when a researcher’s expectations or
preferences about the outcome of a study influence the results obtained.Demand characteristics—clues participants discover about the purpose of the study
that suggest how they should respond.Single-blind procedure—research design in which participants don’t know whether
they are in the experimental or control group.Double-blind procedure—research design in which neither the experimenter nor the
participants know who is in the experimental group and who is in the control group.Placebo—a physical or psychological treatment given to the control group that resem-
bles the treatment given to the experimental group, but that contains no active ingredient.Placebo effect—a response to the belief that the independent variable will have an
effect, rather than the actual effect of the independent variable, which can be a con-
founding variable.Research Methods 63Table 6.1 Overview of Research Methods
Research
Method Description Key Strength Major Weakness
Experiment Manipulation of an Can establish cause and Ability to generalize to
independent variable (IV) effect relationships between real world behavior can
under controlled conditions the IV and the DV be limited
and measurement of its
effects on a dependent
variable (DV)
Quasi- Measurement of a DV when Can provide strong evidence Lack of random assignment
experiment random assignment to suggesting cause and effect can weaken conclusions
groups is not possible relationships
Naturalistic Careful observations of Provides descriptive data Loss of experimental
observation humans or animals in about behavior with control
real-life situations wide applicability
Surveys and Obtain large samples of Ease of administration, Distorted results because
Tests abilities, beliefs, or scoring, and statistical of sampling error, poorly
behaviors at a specific analysis phrased questions, and
time and place response biases
Case studies Intensive investigation of Provide detailed descriptive May not be representative
the behavior and mental data and analyses of new, of phenomena
processes associated with a complex, or rare phenomena
specific person or situation