The scientific notion of causality implies that we can never prove that X causes Y. At best, we can only infer that X is one of the causes of Y in that it makes the occurrence of Y probable.
Three conditions must be satisfied before casual inferences can be made:
- concomitant variation, which implies that X and Y must vary together in a hypothesized way
- timed order of occurrence of variables, which implies that X must precede Y
- a lemon nation of other possible casual factors, which implies that competing explanations must be ruled out
In designing an experiment, it is important to consider internal and external validity. Internal validity refers to whether the manipulation of the independent variables actually cause the effects of the dependent variables. External validity refers to the realizability of experimental results.
For the experiment to be valid, the researcher must control the threats imposed by extraneous variables, such as:
- history
- maturation
- testing (main and interactive testing effects)
- instrumentation
- statistical regression
- selection bias
- mortality
- randomization
- matching
- statistical control
- design control
- pre-experimental
- true experimental
- quasi-experimental
- statistical
Although experiments have limitations in terms of time, cost, and administration, they are becoming increasingly popular in marketing. Test marketing is an important application of experimental design.
The internal and external validity of field experiments conducted overseas is generally lower in the United States. The level of development in many countries is lower, and the researcher lacks control over many of the marketing variables. The ethical issues involved in conducting casual research include describing the purpose of the experiment. Debriefing can be used to address some of these issues. The Internet and computers are very useful in the design and implementation of experiments.
Causality -- when the occurrence of X increases the probability of the occurrence of Y
concomitant variation -- a condition for inferring causality that requires the extent to which a cause,X, and an effect,Y, occurred together or buried together is predicted by the up office this under consideration
independent variables -- variables that are manipulated by the researcher and whose effects are measured and compared
test units -- individuals, organizations, or other entities whose response to independent variables or treatments is being studied
dependent variables -- variables that measure the effect of the independent variables on the test units
extraneous variables -- variables, other than the independent variables, that influence the response of the test units
experiment -- the process of manipulating one or more independent variables and measuring their effect on one or more dependent variables, while controlling for the extraneous variables
experimental design -- a set of experimental procedures specifying:
- the test units and sampling procedures
- independent variables
- dependent variables
- how to control the extraneous variables
external validity -- a determination of whether the cause and effect relationships found in the experiment can be generalized
history (H) -- specific events that are external to the experiment but occur at the same time as the experiment
maturation (MA) -- an extraneous variable attributable to changes in the test units themselves that occur with the passage of time
Main testing effect (MT) -- an effect of testing occurring when a prior observation affects a later observation
interactive testing effect (IT) -- an effect in which a prior measurement affects the testing its response to the independent variable
instrumentation (I) -- an extraneous variable involving changes in the measurable instrument or in the observers were scores themselves
statistical regression (SR) -- an extraneous variable that occurs when testing its with extreme scores move closer to the average score during the course of the experiment
selection bias (SB) -- an extraneous variable attributable to the improper assignment of test units to treatment conditions
mortality (MO) -- an extraneous variable attributable to the loss of test units while the experiment is in progress
confounding variables -- synonymous with extraneous variables, used to illustrate that extraneous variables can confound the results by influencing the dependent variable
randomization -- 1 method of controlling extraneous variables that involves randomly assigning test units to experimental groups by using random numbers. Treatment conditions are also randomly assigned to experimental groups
matching -- 1 method of controlling extraneous variables that involves matching test units on a set of key background variables before assigning them to the treatment conditions
statistical control -- 1 method of controlling extraneous variables by measuring the extraneous variables and adjusting for their effects through statistical methods
design control -- 1 method of controlling extraneous variables that involves using specific experimental designs
pre-experimental designs -- designs that do not control for extraneous factors by randomization
true experimental designs -- experimental designs distinguished by the fact that the researcher can randomly assigned test units to experimental groups and also randomly assigned treatments to experimental groups
quasi-experimental designs -- designs that apply part of the procedures of true experimentation but lack full experimental control
statistical design -- designs that allow for the statistical control and analysis of external variables
one-shot case study -- a pre-experimental design in which a single group of test units is exposed to treatment X, and then a single measurement on the dependent variable is taken
one group pre-test - posttest design -- a pre-experimental design in which a group of test units is measured twice
static group -- a pre-experimental design in which there are two groups: the experimental group (EG), which is exposed to the treatment, and the control group (CG). Measurements on both groups are made only after the treatment, and test units are not assigned at random
pre-test - posttest control group design -- a true experimental design in which the experimental group is exposed to the treatment at the control group is not. Pre-test and posttest measurements are taken on both groups
posttest only control group design -- a true experimental design in which the experimental group is exposed to the treatment but the control group is not and no pretest measure is taken
Solomon four-group design -- a true experimental design that explicitly controls for interactive testing effects, in addition to controlling for all the other extraneous variables
time series design -- a quasi-experimental design that involves periodic measurements on the dependent variable for a group of test units. Then, the treatment is administered by the researcher or occurs naturally. After the treatment, periodic measurements are continued in order to determine the treatment effect
multiple time series design -- a time series design that includes another group of test units to serve as a control group
randomized block design -- a statistical design in which to test units are blocked on the basis of on external variable to ensure that the various experimental and control groups are matched closely on that variable
Latin square design -- a statistical design allows for the statistical control of two non-interacting external variables in addition to the manipulation of the independent variable
factorial design -- a statistical experimental design that is used to measure the effects of two or more independent variables at various levels and to allow for interactions between variables
laboratory environment -- an artificial setting for experimentation in which the researcher conducts the desired conditions
field environment -- an experimental location set in the actual market conditions
demand artifacts -- the respondents attempt to guess the purpose of the experiment and respond accordingly
test marketing -- an application of a controlled experiment done in limited, but carefully selected, test markets. It involves a replication of the planned national marketing program for a product in the test markets
test markets -- a carefully selected part of the marketplace that is particularly suitable for testmarketing
standard test market -- a test market in which the product is sold through regular distribution channels. For example, no special considerations are given to product simply because they are being testmarketed
controlled test market -- a testmarketing program conducted by an outside research company in field experimentation. The research company guarantees distribution of the product and retail outlet that represent a predetermined percentage of the market
simulated test market -- a quasi-test market in which respondents are preselected, then interviewed and observed on their purchases and attitudes toward the product
debriefing -- after the experiment, informing test subjects with the experiment was about and how they experimental manipulations were performed
