Chapter 12 - Experimental Research
Reducing demand characteristics
Use an experimental disguise, isolate experimental subjects, use a blind experimental administrator, administer only one experimental treatment level to each subject
Time series design
Used for an experiment investigating long-term structural changes
Extraneous variables
Variables that naturally exist in the environment that may have some systematic effect on the dependent variable
Experimental treatment
the term referring to the way an experimental variable is manipulated
Blocking variables
A categorical variables that is not manipulated like an experimental variable but is included in the statistical analysis of experiments
Randomized-block design
A design that attempts to isolate the effects of a single extraneous variable by blocking out its effects in the dependent variable
Placebo
A false experimental confiarían aimed at creating the impression of the effect
Control group
A group of subject who no experimental treatment is administered
Experimental group
A group of subjects to whom an experimental treatment is administered
Testing effects
A nuisance effect occurring when the initial measurement or test alerts or primes subjects in a way that affects their response to ej experimental trestments
Instrumentation effect
A nuisance that occurs when a change in the wording of questions, a change in interviewers, or a change in other procedures causes a change in the dependent variable
Manipulation check
A validity test of an experimental manipulation to make sure that the manipulation does produce differences in the independent variable
Basic experimental design
An experiment design in which only one variable is manipulated
Completely randomized design
An experimental design that uses a random process to assign subjects to treatment levels of an experimental variable
Counterbalancing
Attempts to eliminate the confounding effects of order of presentation by requiring that one fourth of the subjects be exposed to treatment A first, one fourth to treatment B first, one fourth to treatment C first, and finally one fourth to treatment D first.
Demand effect
Occurs when demand characteristics actually affect the dependent variable
History effect
Occurs when some change other than the experimental treatment occurs during the course of an experiment that affects the dependent variable
Factorial experimental design
Investigation of the interaction of two or more independent variables
Within subjects design
Involves repeated measures because with each treatment the same subject is measured
Nuisance variables
Items that may affect the dependent measure but are not a primary interest
Experimental design elements
Manipulation of the independent variable, selection and measurement of the dependent variable, selection and assignment of experimental subjects, control over extraneous variables
Matching
Matching the respondents in the basis of pertinent background information by assigning subjects in a way that their characteristics are the same in each group
Constancy of conditions
Means that subjects in all experimental groups are exposed to identical conditions except for the differing experimental treatments
Confound
Means that there is an alternative explanation beyond the experimental variables for any observed differences in the dependent variable
Systematic or non sampling error
Occurs if the sampling units in an experimental cell are somehow different than the units in another cell, and this difference affects the dependent variable
Mortality effect (sample attrition)
Occurs when some subjects withdraw from the experiment before it is completed
Experimental condition
One of the possible levels of an experimental variable manipulation
Compromise designs
One that falls short of assigning subjects or treatments randomly to experimental groups
Hawthorne effect
People will perform differently from normal when they know they are experimental subjects
Cohort effect
Refers to a change in the dependent variable that occurs because members of one experimental group experienced different historical situations than members of other experimental groups
Cell
Refers to a specific treatment combination associated with an experimental group
Field experiments
Research projects involving experimental manipulations that are implemented in a natural environment
Selection effect
Sample bias from differential selection of respondents for experimental groups
Basic experimental design
Single independent variable is manipulated to observe its effect on a single dependent variable
Tachistoscope
Device that controls the amount of time a subject is exposed to a visual image
Interaction effect
Differences in dependent variable means due to a specific combination of independent variables
Between subjects design
Each subject only receives only one treatment combination
Maturation effect
Effects that are a function of time and the naturally occurring events that coincide with growth and experience
Internal validity
Exists to the extent that an experimental variable is truly responsible for any variance in the dependent varisbke
Demand characteristic
Experimental design element or procedure that unintentionally provides subjects with hints about the research hypothesis
Quasiexperimental designs
Experimental designs that do not involve random allocation of subjects to treatment combinations
Repeated measures
Experiments in which an individual subject is exposed to more than one level of an experimental treatment
External validity
The accuracy with which experimental results can be generalized beyond the experimental subjects
Placebo effect
The effect in a dependent variable associated with the psychological impact that goes along with knowledge of some treatment being administered
Main effect
The experimental difference in dependent variable means between the different levels of any single experimental variable
Randomization
The random assignment of subject and treatments to groups; it is one device for equally distributing the effects of extraneous variables to all conditions
Laboratory experiment
The researcher has more complete control over the research setting and extraneous variables
Subjects
The sampling units for an experiment, usually human respondents who provide measures based on the experimental manipulation
Test units
The subjects or entities whose responses to the experimental treatment are measured or observed