Experimental and Control Conditions
The experimental method allows researchers to track down the likely causes of behavior.
Overiew of Steps in an Experiment
Key Concepts Explained
- An experiment allows the researcher to manipulate the variables in a very controlled situation to determine if changes in one variable produces (causes) changes in the other.
- Because there is manipulation in experiments, great care is taken to ensure ethical and humane treatment.
wwwlink: The American Psychological Association's Ethics Guidelines.
This is the heart of the experimental manipulation to determine cause.
- Independent variable is the variable that the experimenter manipulates
- Dependent variable is the variable that is predicted to be influenced by the independent variable.
Key Concepts Explained
One variable (independent variable) is manipulated by the researcher to see what its effect will be on the other variable (dependent variable).
Rules of thumb to decide which is the independent variable and which is the dependent variable;
- The dependent variable depends upon the influence of the independent variable. Look for the one that depends on the other.
- The "If, then" rule: Create a sentence describing the relationship between the variables. If = independent variable, Then = dependent variable. If you get the proper order, the sentence will make sense. Identify which sentence makes the most sense:
If I drink caffeine (IV) when studying, then I will remember more for the test (DV).
If I remember more for the test (IV), then I will drink more caffeine (DV). This second statement just doesn't make good sense. Hence the first "if, then" sentence has correctly identified the independent and dependent variables.
NEED AND EXERCISE RIGHT HERE
wwwlink: Tutorials written by students on conducting research.
wwwlink: Everything you ever wanted to know about designing research.
To establish cause and effect clearly, this step has to be included to eliminate any differences that might exist between groups of subjects and insure that everything is held constant except the manipulation of the independent variable.
The Control Condition is a comparison condition in which the subjects are not exposed to the same treatment as in the experimental condition.
Key Concepts Explained
- Two very similar groups are created by randomly assigning subjects to each group (e.g. flip a coin). This produces two groups that will be roughly equal on any variable, e.g. the same average height, weight, intelligence, income, etc.
- One group becomes the experimental group because it receives the independent variable. The other group, the control group, is treated exactly the same except it does not receive the independent variable.
- Rationale - When we compare the results from the experimental group with the control group and find there are differences between the two groups on the dependent variable, we are now confident that there weren't any preexisting differences between the two groups. Example: If all the subjects with bad driving records were placed in the experimental group and given nicotine, we could not be confident that it was the nicotine that caused the greater number of rear end collisions. However, if we know the groups start out the same, then any difference in the dependent variable has to be due to the effects of the independent variable.
Measures need to be taken to make sure that the researcher's personal expectations don't unduly influence the results of the study.
Key Concepts Explained:
Here are some of the ways in which experiementers keep expectations from influencing the results of the study:
- Single blind study: subjects don't know whether they are in the experimental or the control group.
- Double-blind study: Neither the subjects nor the experimenter know who is in the experimental or control group.
wwwlink: How various biases can make people think bogus therapies work.
wwwlink: Facilitated Communication exposed in double-blind studies.
wwwlink: Experimenter Bias in Hypnosis Performance.
If the steps outlined in this section are done correctly, researchers can make conclusions about cause and effect relationships between variables.
Limitations to the Experimental Method
- The typical subjects in psychological experiments are college students who are not representative of the larger population.
- Because they know they are in an experiment, subjects may act in ways
Comparison of the Different Methods:
|Case Study||Good Source of hypotheses.||Individual may not be representative or typical.|
|Provides in-depth information on individuals.||Difficult to know which subjective interpretation is best.|
|Unusual cases can shed light on situations or problems tha are unethical or impractical to study in other ways.||Allows researcher little or no control of the situation.|
|Naturalistic Observation||Allows description of behavior as it occurs in the natural environment.||Observations may be biased.|
|Often useful in first stages of a research program.||Does not allow firm conclusions on cause and effect.|
|Laboratory Observation||Allows more control than naturalistic observation.||Allows researcher only limited control of the situation.|
|Allows use of sophisticated equipment.||Observation may be biased.|
|Does not allow firm conclusions on cause and effect.|
|Behavior in the laboratory may differ from behavior in the natural environment.|
|Test||Yields information on personality traits, emotional states, aptitudes, abilities.||Difficult to construct tests that are valid and reliable.|
|Survey||Provides largest amount of information on large groups of people.||If sample is nonrepresentative or biased, it may be impossible to generalize from the results.|
|Responses may be inaccurate or untrue.|
|Correlational Study||Shows whether two or more variables are related.||Does not permit identification of cause and effect.|
|Allows general predictions.|
|Experiment||Allows researcher to control situation.||Situation is artificial, and results my not generalize well to the real world.|
|Permits researcher to identify cause and effect.||Sometimes difficult to avoid experimenter effects.|