Presentation on theme: "Science answers questions with experiments. IIt is a controlled method of observation in which the value of one or more independent variables is changed."— Presentation transcript:
Science answers questions with experiments
IIt is a controlled method of observation in which the value of one or more independent variables is changed to assess its causal effect on one or more dependent variables (Monette et al, 1994) TThe experimental method involves manipulating one variable to determine if changes in one variable cause changes in another variable. This method relies on controlled methods, random assignment and the manipulation of variables to test a hypothesis. (Kendra Cherry)
Proves the direct cause-and-effect relationship between two variables. For instance: Why some adults are more successful than their peers or Why some children are more active than others.
AdvantagesDisadvantages Best establishes cause and effect relationships Adjustability/ flexibility Lack of “ reality” Unrepresentative samples
1. Pre-experimental designs (low degree of control) 2. True experimental designs (high degree of control) 3. Quasi-experimental designs (medium degree of control)
They are not characterized by random selection of participants from a population. They do not include a control group. They allow little or no control over extraneous variables that might be responsible for outcomes other than what the researcher intended. There is no comparison between an equivalent non- treatment group is made
A parent uses an old folk remedy (wearing garlic around the neck) toward off the evil spirits associated with a child’s cold. This is the weakest type of experimental conclusion to reach because there is virtually no comparison to show that the garlic worked better than anyhing else, or better than nothing at all for that matter. There is simply no control over other factors.
The One-Shot Case Study The One- Group Pretest posttest Study The Static Comparison/ Posttest only Design with Nonequivalent Groups
True experimental design is regarded as the most accurate form of experimental research, in that it tries to prove or disprove a hypothesis mathematically, with statistical analysis. For some of the physical sciences, such as physics, chemistry and geology, they are standard and commonly used. For social sciences, psychology and biology, they can be a little more difficult to set up.
For an experiment to be classed as a true experimental design, it must fit all of the following criteria. The sample groups must be assigned randomly.randomly There must be a viable control group.control group Only one variable can be manipulated and tested.variablemanipulated The tested subjects must be randomly assigned to either control or experimental groups.
The results of a true experimental design can be statistically analyzed and so there can be little argument about the results.results True experimental design usually gives a yes or no answer.
Firstly, they can be almost too perfect, with the conditions being under complete control and not being representative of real world conditions.complete control For psychologists and behavioral biologists, for example, there can never be any guarantee that a human or living organism will exhibit ‘normal’ behavior under experimental conditions. They are difficult and expensive to set up.
Pretest-posttest Control Group Design Posttest Only Control Group Design The Solomon Four Group Design
Internal validity is synonymous with control.
External Validity is synonymous with generalizability.
Interaction of testing treatment Interaction of selection and treatment Reactive Arrangements Multiple Treatment Interference
Quasi-experimental design is a form of experimental research used extensively in the social sciences and psychology. Designs for which it is impossible randomly assign participants to all groups are called quasi experimetal designs because they are not truly experimental.
Especially in social sciences, where pre- selection and randomization of groups is often difficult, they can be very useful in generating results for general trends.randomizationresults E.g. if we study the effect of maternal alcohol use when the mother is pregnant, we know. that alcohol does harm embryos. A strict experimental design would include that mothers were randomly assigned to drink alcohol. This would be highly illegal because of the possible harm the study might do to the embryosstrict experimental design
So what researchers do is to ask people how much alcohol they used in their pregnancy and then assign them to groups. In addition, without extensive pre-screening and randomization needing to be undertaken, they do reduce the time and resources needed for experimentation.
Without proper randomization, statistical tests can be meaningless. A quasi experiment constructed to analyze the effects of different educational programs on two groups of children, for example, might generate results that show that one program is more effective than the other. These results will not rigorous statistical. The researcher also need to control other factors that may have affected the results. This is really hard to do properly.control One group of children may have been slightly more intelligent or motivated. Without some form of pre- testing or random selection, it is hard to judge the influence of such factors.
Pretest-Posttest Nonequivalent Group Time Series Design Nonequivalent Before- After Design