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Chapter 10

PSY309 - Chapter 10 Notes

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John Kloppenbord

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Chapter X: Non-Experimental & Quasi-Experimental Strategies Non-Equivalent Group, Pre-Post, and Developmental Designs 10.1 Non-Experimental & Quasi-Experimental Research Strategies Five basic research strategies: experimental, non-experimental, quasi-experimental, correlational, and descriptive. A researcher can often devise a research strategy (a method of collecting data) that is similar to an experiment but fails to satisfy at least one of the requirements of a true experiment. Such studies are generally called non-experimental or quasi-experimental research studies. Although these studies resemble experiments, they always contain a confounding variable or other threat to internal validity that is an integral part of the design and simply cannot be removed. The existence of a confounding variable means that these studies cannot establish unambiguous cause-and-effect relationships and, therefore, are not true experiments. The distinction between the non-experimental research strategy and the quasi- experimental research strategy is the degree to which the research strategy limits confounding and controls threats to internal validity. If a research design makes little or no attempt to minimize threats, it is classified as non- experimental. A quasi-experimental design, on the other hand, makes some attempt to minimize threats to internal validity and approaches the rigor of a true experiment. A quasi-experimental design, on the other hand, makes some attempt to minimize threats to internal validity and approaches the rigor of a true experiment. The fact that quasi-experimental and non-experimental studies are not true experiments does not mean that they are useless or even second-class research studies. Non-experimental and quasi-experimental studies often look like experiments in terms of the general structure of the research study. A non-experimental or quasi-experimental study typically involves comparing groups of scores. One variable is used to create groups or conditions, then a second variable is measured to obtain a set of scores within each condition. The different groups or conditions are not created by manipulating an independent variable. Groups are usually defined in terms of a pre-existing participant variable or in terms of time. Two methods of defining groups produce two general categories of non-experimental and quasi-experimental designs: 1. Between-subjects designs, also known as non-equivalent group designs. 2. Within-subjects designs, also known as pre-post designs. The non-experimental research strategy makes little or non attempt to control threats to internal validity whereas the quasi-experimental research strategy attempts to limit threats to internal validity. Both strategies, like true experiments, typically involve a comparison of groups or conditions. However, these two strategies use a non-manipulated variable to define the groups or conditions being compared. The non-manipulated variable is usually a participant variable (such as male versus female) or a time variable (such as before versus after treatment). 10.2 Between-Subjects Non-Experimental & Quasi-Experimental Designs: Non- Equivalent Group Designs Between-subjects experimental design refers to a method of comparing two or more treatment conditions using a different group of participants in each condition. A common element to between-subjects experiments is the control of participant variables by assigning participants to specific treatment conditions. The goal is to balance or equalize participant variables across treatment conditions by using a random process or by deliberately matching participants. Note that the researcher attempts to create equivalent groups of participants by actively deciding which individuals go into which groups. When the researcher cannot use random assignment or matching to balance participant variables across groups, there is no assurance that the two groups are equivalent. In this situation, the research study is called a non-equivalent group design. A non-equivalent group design is a research study in which the different groups of participants are formed under circumstances that do not permit the researcher to control the assignment of individuals to groups, and the groups of participants are, therefore, considered non-equivalent. Specifically, the researcher cannot use random assignment to create groups of participants. A non-equivalent group design has a built-in threat to internal validity that precludes an unambiguous cause-and-effect explanation: assignment bias. Assignment bias occurs whenever the assignment procedure produces groups that have different participant characteristics In a non-equivalent group design, there is no random assignment and there is no assurance of equivalent groups. Three common examples of non-equivalent group designs: (1) the differential research design, (2) the post-test-only non-equivalent control group design, and (3) the pretest- posttest non-equivalent control group design. Non-equivalent group research involves no manipulation but simply attempts to compare pre-existing groups that are defined by a particular participant variable A research study that simply compares pre-existing groups is called a differential research design because its goal is to establish differences between the pre-existing groups. This type of study is often called ex post facto research because it looks at differences after the fact; that is, at differences that already exist between groups. Differential research design makes no attempt to control the threat of assignment bias; it is classified as a non-experimental research design. A research study that simply compares pre-existing groups is called a differential research design. A differential study uses a participant characteristic such as gender, race, or personality to automatically assign participants to groups. The researcher does not randomly assign individuals to groups. A dependent variable is then measured for each participant to obtain a set of scores within each group. The goal of the study is to determine whether the scores for one group are consistently different from the scores of another group. Differential research is classified as a non-experimental research design. Many researchers place differential research in the same category as correlational research based on their similarities. In differential and correlational studies, a researcher simply observes two naturally occurring variables without any interference or manipulation. The subtle distinction between differential research and correlational research is whether or not one of the variables is used to establish separate groups to be compared. In differential research, participant differences in one variable are used to create separate groups, and measurements of the second variable are made within each group. The researcher then compares the measurements for one group with the measurements of another group, typically looking at mean differences between groups. A correlational study treats all participants as a single group and simply measures the two variables for each individual. Both designs allow researchers to establish the existence of relationships and to describe relationships between variables, but neither design permits a cause-and-effect explanation of the relationship.Posttest-Only Non-Equivalent Control Group Design Non-equivalent groups are commonly used in applied research situations in which the goal is to evaluate the effectiveness of a treatment administered to a pre-existing group of participants. A second group of similar but non-equivalent participants is used for the control condition. The researcher uses pre-existing groups and does not control the assignment of participants to groups. The researcher does not randomly assign individuals to groups. A non-equivalent control group design uses pre-existing groups, one of which serves in the treatment condition and the other in the control condition. The researcher does not randomly assign individuals to groups. One common example of a non-equivalent control group design is called a posttest-only non-equivalent control group design. This type of study is also called a static group comparison. In this type of design, one group of participants is given a treatment and then is measured after the treatment, The scores for the treated group are then compared with the scores from a non-equivalent group that has not received the treatment. A posttest-only non-equivalent control group design, also known as a static group comparison, compares two non-equivalent groups of participants. One group is observed (measured) after receiving a treatment, and the other group is measured at the same time but receives no treatment. This is an example of a non-experimental research design. The posttest-only non-equivalent control group design does not address the threat of assignment bias; it is considered a non-experimental design. Pretest-Only Non-Equivalent Control Group Design A much stronger version of the non-equivalent control group design is often called a pretest-posttest non-equival
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