Research designs Research designs Quantitative Research Designs

Experimental research: Experimental research is concerned with cause- and-effect relationships. All experimental studies involve manipulation of the independent variable (cause) and measurement of the dependent variable (effect) Experimental research is concerned with cause- and-effect relationships. All experimental studies involve manipulation of the independent variable (cause) and measurement of the dependent variable (effect)

In experimental studies as, well as in other types of research, the researcher is interested in controlling extraneous variables that may influence study results. Extraneous variables: are those variables that the researcher is not able to control, and that may influence the results of a study. These variables are also called study limitations. In experimental studies as, well as in other types of research, the researcher is interested in controlling extraneous variables that may influence study results. Extraneous variables: are those variables that the researcher is not able to control, and that may influence the results of a study. These variables are also called study limitations.

In experimental studies, the researcher is trying to establish a cause-and-effect relationship. The internal validity of an experimental design concerns the degree to which changes in the dependent variables (effect) can be attributed to the independent variable (cause). In experimental studies, the researcher is trying to establish a cause-and-effect relationship. The internal validity of an experimental design concerns the degree to which changes in the dependent variables (effect) can be attributed to the independent variable (cause). The external validity Concerns the degree to which study results can be generalized to other people and other settings. The external validity Concerns the degree to which study results can be generalized to other people and other settings.

Threats to internal validity: 1.Selection bias: When the results are due to subject differences before the independent variables was manipulated. Occur when subjects are not randomly assigned to experimental and comparison group. 2. History: Occurs when some event other than the experimental treatment occurs during the course of a study, and this event influences the dependent variable.

3. Maturation: becomes a threat when changes that occur within the subjects during an experimental study influence the study results. People may become older, taller, or sleepier from the time of the pretest to the post test. 3. Maturation: becomes a threat when changes that occur within the subjects during an experimental study influence the study results. People may become older, taller, or sleepier from the time of the pretest to the post test. 4. Testing: the testing threat may occur in studies where a pretest is given or where a pretest is given or where subjects have knowledge of baseline data. Testing refers to the influence of the pretest or knowledge of baseline data on the post test scores. 4. Testing: the testing threat may occur in studies where a pretest is given or where a pretest is given or where subjects have knowledge of baseline data. Testing refers to the influence of the pretest or knowledge of baseline data on the post test scores.

5. Instrumentation change: Involves the difference between the pretest and posttest measurement caused by a change in the accuracy of the instrument or the judges ratings, rather than as a result of the experimental treatment. 5. Instrumentation change: Involves the difference between the pretest and posttest measurement caused by a change in the accuracy of the instrument or the judges ratings, rather than as a result of the experimental treatment. 6. Mortality: The mortality threats occurs when the subject dropout rate is different between the experimental and comparison group. 6. Mortality: The mortality threats occurs when the subject dropout rate is different between the experimental and comparison group.

Threats to external validity: 1. Hawthorn effect: the Hawthorne effect occurs when study participant respond in a certain manner because they are aware that they are being observed. 1. Hawthorn effect: the Hawthorne effect occurs when study participant respond in a certain manner because they are aware that they are being observed. 2. Experimenter effect: is a threat to study results that occurs when researcher characteristics or behaviors influence subject behaviors. 2. Experimenter effect: is a threat to study results that occurs when researcher characteristics or behaviors influence subject behaviors. 3.Reactive effect of the pretest: which is sometimes called the measurement effect that occurs when subjects have been sensitized to the treatment through taking the pretest. 3.Reactive effect of the pretest: which is sometimes called the measurement effect that occurs when subjects have been sensitized to the treatment through taking the pretest.

Symbolic presentation of research design: Symbolic presentation of research design: R = random assignment of subjects to group. R = random assignment of subjects to group. O= Observation or measurement of dependent variable O= Observation or measurement of dependent variable X= experimental treatment or intervention. X= experimental treatment or intervention.

Random assignment: is a procedure that ensures that each subjects has an equal chance of being assigned or placed in any of the groups in an experiment study. Random assignment: is a procedure that ensures that each subjects has an equal chance of being assigned or placed in any of the groups in an experiment study.

Types of the experimental designs: Are those in which the researcher has a great deal of control over the research situation. There are three criteria for a true experimental design: Are those in which the researcher has a great deal of control over the research situation. There are three criteria for a true experimental design: 1.The researcher manipulates the experimental variables (s). 2. At least one experimental and one comparison group are included in the study. 3. Subjects are randomly assigned to either the experimental or the comparison group.

Note the term manipulation: means that the independent, or experimental, variable is controlled by the researcher. Note the term manipulation: means that the independent, or experimental, variable is controlled by the researcher.

1. TRUE EXPERIMENTAL DESIGN: 1. TRUE EXPERIMENTAL DESIGN: 1. Pretest-post test control group design: is probably the most frequently used experimental design 1. Pretest-post test control group design: is probably the most frequently used experimental design R O1 X O2 (Experimental group) R O1 X O2 (Experimental group) R OI O2 ( Comparison group) R OI O2 ( Comparison group)

2. Post test-only control group design: R X O1 (Experimental group) R X O1 (Experimental group) R O2 ( Comparison group) R O2 ( Comparison group)

Solomon four – group design: Solomon four – group design: RO1 X O2 (Experimental group1) RO1 X O2 (Experimental group1) RO1 O2 (Comparison group 1) RO1 O2 (Comparison group 1) R x O2 (Experimental group 2) R x O2 (Experimental group 2) R O2 (Comparison group 2) R O2 (Comparison group 2)

11. QUASIEXPERIMENTAL DESIGNS: are those in which there is either no comparison group or subjects are not randomly assigned to groups. 11. QUASIEXPERIMENTAL DESIGNS: are those in which there is either no comparison group or subjects are not randomly assigned to groups. 1.Nonequivalent control group design: O1 X O2 (Experimental group) O1 X O2 (Experimental group) O1 O2 (Comparison group) O1 O2 (Comparison group) 2. Time – series design: O1 O2 O3 X O4 O5 O6 O1 O2 O3 X O4 O5 O6

111. PREEXPERIMENTAL DESIGN: 111. PREEXPERIMENTAL DESIGN: 1. One shot case study: A single group is exposed to an experimental treatment and observed after the treatment. 1. One shot case study: A single group is exposed to an experimental treatment and observed after the treatment. X O X O 2. One group pretest-post test design: Provides a comparison between a group of subjects before and after the experimental treatment. O1 X O2 O1 X O2