INTRODUCTION
Unlike a descriptive study, an experiment is a study in which a treatment, procedure, or kegiatan is intentionally introduced and a result or outcome is observed. The American Heritage Dictionary of the English Language defines an experiment as “A test under controlled conditions that is made to demonstrate a known truth, to examine the validity of a hypothesis, or to determine the efficacy of something previously untried.”
True experiments have four elements: manipulation, control, random, assignments, and random selection. The most important of these elements are manipulation and control. Manipulation means that something is purposefully changed by the researcher in the environment. Control is used to prevent outside factors from influencing the study outcome. When something is manipulated and controlled and then the outcome happens, it makes us more confident that the manipulation “caused” the outcome. In addition, experiments involve highly controlled and systematic procedures in an effort to minimize error and bias which also increases our confidence that the manipulation “caused” the outcome.
DISCUSSION
A. Definition of True Experiment
A true experimental design is one in which the researcher manipulates the Independent Variable (or variables) to observe its effect on some behavior or cognitive process (the dependent variable) while using random assignment of participants to groups in order to control external factors from influencing the results. Without both manipulation of the IV and random assignment of participants, you do not have a true experimental design and, as a result, cannot establish cause and effect.
True experimental design makes up for the shortcomings of the two designs previously discussed. They employ both a control group and a means to measure the change that occurs in both groups. In this sense, we attempt to control for all confounding variables, or at least consider their impact, while attempting to determine if the treatment is what truly caused the change. The true experiment is often thought of as the only research method that can adequately measure the cause and effect relationship.
True experiments are considered the most accurate form of experimental research. They are commonly used in the physical sciences, such as chemistry, geology and physics, to prove or disprove a hypothesis, or theory, but are more difficult to apply to social sciences, such as biology or psychology. The characteristic feature of a true experiment is that subjects are randomly assigned. This means that any difference between them is purely due to chance. For simplicity, just one variable is manipulated and tested.
B. Characteristic of True Experiment
1. Time order of variable
2. Manipulation of the independent variable
3. Relationships between variable
4. Control of rival (alternative) hypothesis
5. Use of a control group
6. Random sampling and random assignment
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C. Bias and Assignments
In a true experiment, randomization means that it is unlikely that one subject is significantly superior or inferior to another. This means that variables associated with individuals are not sources of constant or systematic error, although there still may an element of bias in the overall design of the experiment.
Randomization can be achieved by tossing a coin, rolling a die or using a computerized random number generator to assign treatments to subjects. In quasi experiments, nonrandom assignment - based on first-come, first-served, perceived ability or some other criterion - can significantly influence the outcome of the experiment, particularly if differences in immeasurable characteristics, such as intelligence, exist among subjects.
D. Components of Experimental Research Design
1. The Manipulation of Predictor Variables
In an experiment, the researcher manipulates the factor that is hypothesized to affect the outcome of interest. The factor that is being manipulated is typically referred to as the treatment or intervention. The researcher may manipulate whether research subjects receive a treatment (e.g., antidepressant medicine: yes or no) and the level of treatment (e.g., 50 mg, 75 mg, 100 mg, and 125 mg).
Suppose, for example, a group of researchers was interested in the causes of maternal employment. They might hypothesize that the provision of government-subsidized child care would promote such employment. They could then design an experiment in which some subjects would be provided the option of government-funded child care subsidies and others would not. The researchers might also manipulate the value of the child care subsidies in order to determine if higher subsidy values might result in different levels of maternal employment.
2. Random Assignment
· Study participants are randomly assigned to different treatment groups
· All participants have the same chance of being in a given condition
· Participants are assigned to either the group that receives the treatment, known as the "experimental group" or "treatment group," or to the group which does not receive the treatment, referred to as the "control group"
· Random assignment neutralizes factors other than the independent and dependent variables, making it possible to directly infer cause and effect
3. Random Sampling
Traditionally, experimental researchers have used convenience sampling to select study participants. However, as research methods have become more rigorous, and the problems with generalizing from a convenience sample to the larger population have become more apparent, experimental researchers are increasingly turning to random sampling. In experimental policy research studies, participants are often randomly selected from kegiatan administrative databases and randomly assigned to the control or treatment groups.
E. Validity of Results
The two types of validity of experiments are internal and external. It is often difficult to achieve both in social science research experiments.
1. Internal Validity
· When an experiment is internally valid, we are certain that the independent variable (e.g., child care subsidies) caused the outcome of the study (e.g., maternal employment)
· When subjects are randomly assigned to treatment or control groups, we can assume that the independent variable caused the observed outcomes because the two groups should not have differed from one another at the start of the experiment
· For example, take the child care subsidy example above. Since research subjects were randomly assigned to the treatment (child care subsidies available) and control (no child care subsidies available) groups, the two groups should not have differed at the outset of the study. If, after the intervention, mothers in the treatment group were more likely to be working, we can assume that the availability of child care subsidies promoted maternal employment
One potential threat to internal validity in experiments occurs when participants either drop out of the study or refuse to participate in the study. If particular types of individuals drop out or refuse to participate more often than individuals with other characteristics, this is called differential attrition. For example, suppose an experiment was conducted to assess the effects of a new reading curriculum. If the new curriculum was so tough that many of the slowest readers dropped out of school, the school with the new curriculum would experience an increase in the average reading scores. The reason they experienced an increase in reading scores, however, is because the worst readers left the school, not because the new curriculum improved students' reading skills.
2. External Validity
· External validity is also of particular concern in social science experiments
· It can be very difficult to generalize experimental results to groups that were not included in the study
· Studies that randomly select participants from the most diverse and representative populations are more likely to have external validity
· The use of random sampling techniques makes it easier to generalize the results of studies to other groups
For example, a research study shows that a new curriculum improved reading comprehension of third-grade children in Iowa. To assess the study's external validity, you would ask whether this new curriculum would also be effective with third graders in New York or with children in other elementary grades.
Glossary terms related to validity:
F. Ethics
It is particularly important in experimental research to follow ethical guidelines. Protecting the health and safety of research subjects is imperative. In order to assure subject safety, all researchers should have their project reviewed by the Institutional Review Boards (IRBS). The National Institutes of Healthsupplies strict guidelines for project approval. Many of these guidelines are based on the Belmont Report.
The basic ethical principles:
· Respect for persons -- requires that research subjects are not coerced into participating in a study and requires the protection of research subjects who have diminished autonomy
· Beneficence -- requires that experiments do not harm research subjects, and that researchers minimize the risks for subjects while maximizing the benefits for them
· Justice -- requires that all forms of differential treatment among research subjects be justified
G. Advantages of True Experiment
1. Reliable Results
Researchers collect data during the experiment and subject this to statistical analysis to determine the significance of their findings. Whether in the physical sciences or the social sciences, true experiment results are considered reliable because they lend themselves to such statistical study.
2. Causality
The biggest advantage of a true experiment is that it is the only experimental design that allows researchers to determine the cause and effect relationship between two factors. The factor that a researcher modifies is known as the independent variable and the effect he seeks to observe is called the dependent variable. For example, if a researcher studies the occurrence of cancer in people who smoke, existence of the disease is the dependent variable and smoking is the independent variable. Performing a true experiment helps the scientist study the nature of the relationship between the dependent and independent variable.
3. Control Groups
In a true experiment, the researcher uses two groups: an experimental group and a control group. The purpose of the control group is to account for extraneous factors other than the independent variable that may have an influence on the experimental results. In such experimental designs, researchers assign subjects randomly to either the experimental or control group. Continuing with the cancer research example, the scientist assigns both male and female subjects of different age groups randomly to either the experimental or control group. Randomization removes the influence of these extraneous factors such as sex and age on the occurrence of cancer and helps the researcher focus on the relationship between smoking and cancer.
CONCLUSION
True experiments must have at least three things:
· Two comparison groups (in the simplest case, an experimental and a control group) Comparison/control group – do not get confused.
· Variation in the independent variable before assessment of change in the dependent variable
· Random assignment to the two (or more) comparison groups.
True experiments must have at least one experimental group (subjects who receive some treatment) and at least one comparison group (subjects to whom the experimental group can be compared). All true experiments have a posttest—that is, measurement of the outcome in both groups after the experimental group has received the treatment. Many true experiments also have pretests that measure the dependent variable prior to the experimental intervention.
REFERENCES
http://www.uic.edu/classes/socw/socw560/EXPERMT/sld008.htm
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