Terms in this set (29)
3 Conditions for Causality
1. Concomitant variation
2. Time order of occurrence
3. Absence of other possible causal factors
the extent to which a cause, X, and an effect, Y, occur together or vary together in the way predicted by the hypothesis under consideration.
o Changes occurs/vary together
Time order of occurrence
states that the causing event must occur either before or simultaneously with the effect; it cannot occur afterwards.
o The cause has to come before or during the effect
Absence of other possible causal factors
the factor or variable being investigated should be the only possible causal explanation.
o No other variables that might have an effect
the extraneous variables are controlled, can provide strong evidence on all three conditions for causality.
are variables or alternatives that are manipulated and whose effects are measured and compared, e.g., price levels.
are individuals, organizations, or other entities whose response to the independent variables or treatments is being examined, e.g., consumers or stores.
are the variables which measure the effect of the independent variables on the test units, e.g., sales, profits, and market shares.
are all variables other than the independent variables that affect the response of the test units, e.g., store size, store location, and competitive effort.
is a set of procedures specifyingthe test units and how these units are to be divided into homogeneous subsamples;what independent variables or treatments are to be manipulated;what dependent variables are to be measured; and how the extraneous variables are to be controlled.
refers to whether the manipulation of the independent variables or treatments actually caused the observed effects on the dependent variables. Control of extraneous variables is a necessary condition for establishing internal validity.
refers to whether the cause-and-effect relationships found in the experiment can be generalized. To what populations, settings, times, independent variables, and dependent variables can the results be projected?
refers to the random assignment of test units to experimental groups by using random numbers. Treatment conditions are also randomly assigned to experimental groups.
Extraneous variables can be controlled by ____________________.
2 Ways to Control Extraneous Variables
1. Do it in a lab
specific events that are external to the experiment but occur at the same time as the experiment.
changes in the test units themselves that occur with the passage of time.
caused by the process of experimentation. Typically, these are the effects on the experiment of taking a measure on the dependent variable before and after the presentation of the treatment.
The main testing effect (MT)
occurs when a prior observation affects a latter observation.
do not employ randomization procedures to control for extraneous factors.
-the one-shot case study, the one-group pretest-posttest design, and the static-group.
True experimental designs
the researcher can randomly assign test units to experimental groups and treatments to experimental groups.
-the pretest-posttest control group design, the posttest-only control group design, and the Solomon four-group design.
is a series of basic experiments that allow for statistical control and analysis of external variables. Example: Factorial design.
One-Shot Case Study
A single group of test units is exposed to a treatment X.
A single measurement on the dependent variable is taken (01).
There is no random assignment of test units.
The one-shot case study is more appropriate for exploratory than for conclusive research.
One-Group Pretest-Posttest Design
01 X 02
A group of test units is measured twice.
There is no control group.
The treatment effect is computed as
02 - 01.
The validity of this conclusion is questionable since extraneous variables are largely uncontrolled.
Static Group Design
EG: X 01
A two-group experimental design.
The experimental group (EG) is exposed to the treatment, and the control group (CG) is not.
Measurements on both groups are made only after the treatment.
Test units are not assigned at random.
The treatment effect would be measured as 01 - 02.
True Experimental Designs: Pretest-Posttest Control Group Design
EG: R 01 X 02
CG: R 03 04
Test units are randomly assigned to either the experimental or the control group.
A pretreatment measure is taken on each group.
The treatment effect (TE) is measured as:(02 - 01) - (04 - 03).
Posttest-Only Control Group Design
EG : R X 01
CG : R 02
The treatment effect is obtained by
TE = 01 - 02
Except for pre-measurement, the implementation of this design is very similar to that of the pretest-posttest control group design.
consist of a series of basic experiments that allow for statistical control and analysis of external variables and offer the following advantages: Specific extraneous variables can be statistically controlled.
Economical designs can be formulated when each test unit is measured more than once.
Limitations of Experimentation
- Time consuming, particularly In measuring the long-term effects.
- Expensive (experimental group, control group, and multiple measurements)
- Difficult to administer.
- May be impossible to control for the effects of the extraneous variables, particularly in a field environment.
- Competitors may deliberately contaminate the results of a field experiment.