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Chapter 13: Experimental Research

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John Bennett

on 17 January 2013

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Transcript of Chapter 13: Experimental Research

Randomization Random assignment is an important ingredient in experimental research. Every individual who is participating in the experiment has an equal chance of being assinged to any of the experimental or control conditions that are being compared.

Random selection means every member of the population has an equal chance of being selected to be a member of the sample. Characteristics of Experimental Research Uniqueness of Experimental Research Experimental research is unique in that it is the only type that directly attempts to influence a particular variable
Tests hypotheses about cause-and-effect relationships
Strongest research method available for educational researchers to use in determining cause-and-effect Control of Extraneous Variables Researcher has opportunity to exercise far more control than in most forms of research.

Most common ways to control the experiment include:
Holding certain variables constant
Building the variable into the design
Using subjects as their own controls
Analysis of the covariance True Experimental Designs The key ingredient to true experimental design is that subjects are randomly assigned to treatment groups.

Randomization is a powerful technique for controlling the subject characteristics threat to internal validity, which is a major consideration in educational research. Quasi-Experimental Designs The matching-only design differs from random assignment with matching only in that random assignment is not used.
In counterbalanced design, all groups are exposed to all treatments, but in a different order.
A time-series design involves repeated measurements or observations over time, both before and after treatment EDUC 6114
John Bennett Chapter 13: Experimental Research Experiments differ from other types of research in two basic ways:

Comparison of treatments

Direct manipulation of one or more independent variables by the researcher Independent variable is also referred to as the experimental or treatable variable. Dependent variable is also known as known as the criterion or outcome. Refers to the outcome of the experiment Basic idea: "Try something and systematically observe what happens" Poor Experimental Designs Three weak designs that are occasionally used in experimental research include:

One-shot case study design
One-group pretest-posttest design
Static-group comparison design One-shot case study: a single group is exposed to a treatment or event, and its effects are assessed. One-group pretest-posttest design: a single group is measured or observed both before and after exposure to a treatment. Static-group comparison design:
two intact groups receive different treatments. Randomized posttest-only control group design involves two groups formed by random assignment Randomized pretest-posttest control group design differs from the previous only in the use of a pretest. Randomized Solomon four-group design involves random assignment of subjects to four groups, with two being pretested and two that are not. Matching A technique used to increase the likelihood that groups of subjects will be equivalent.

Members of the matched groups are assigned to the experimental and control groups.

Matching may be mechanical or statistical. Mechanical matching is a process of pairing two persons whose scores on a particular variable are similar. Difficult to match on more than 2 or 3 variables
Some subjects must be eliminated from the study when no matches can be found Statistical matching does not necessitate a loss of subjects. Each subject is given a predicted score based on a correlation between the dependent variable and the variable(s) on which the subjects are being matched. Factorial Designs Factorial designs extend the number of relationships that may be examined in an experimental study.
They are modifications of either the posttest-only or pretest-only control groups.
Allows the researcher to study the interaction of an independent variable with one or more other variables. Experimental Research - Critique Categories Purpose/justification
Prior research
Procedures/internal validity
Data analysis
Discussion/interpretations Evaluating the likelihood of Threats to Internal Validity Step 1: Ask: What specific factors are known to affect the dependent variable or may be expected to affect this variable?

Step 2: Ask: What is the likelihood of the comparison groups differing on each of these factors?

Step 3: Evaluate the threats on the basis of how likely they are to have an effect, and plan to control for them. (If the threat cannot be controlled, acknowledge this!) Example Subject characteristics
Attitude of subjects
Implementation To summarize...
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