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