Experimental Research Desing

EXPERIMENTAL RESEARCH QUESTIONS AND DESIGNS
Experimental research is used to answer causal research questions: Does something cause an effect? For example, does a low student-teacher ratio cause higher student achievement?
Experimental research designs include the following:
True experimental (randomized trials) Quasi-experimental
In experimental research, the researcher manipulates orvaries an independent variable and measures its effects on one or more dependent variables. In a true experimental design, the researcher randomly assigns the participants who are being studied (also called the subjects) to two or more comparison groups. Sometimes the comparison groups are referred to as treatment and control groups. Participants in the treatment group receive some type of treatment,such as a special reading program. Participants in the control group do not receive the treatment.
For example, at the beginning of a school year, a researcher randomly assigns all classes in a school district to have either a low student-teacher ratio (small class, the treatment group) or a normal student-teacher ratio (large class, the control group). At the end of the school year, theresearcher measures each student’s achievement using the state assessment and compares the average achievement of students in the two sizes of classes. In this example, class size is the independent variable because class size is being varied or manipulated. Student achievement is the dependent variable because student achievement is being measured.
In a quasi-experimental design, the researcher doesnot randomly assign participants to comparison groups, usually because random assignment is not feasible. To improve a quasi-experimental design, the researcher can match the comparison groups on characteristics that relate to the dependent variable. For example, a researcher selects from a school district 10 classes to have low student-teacher ratios and 10 classes to maintain their current highstudent-teacher ratios. The researcher selects the high-ratio classes based on their similarity to the low-ratio classes in terms of student socioeconomic status, a variable that is related to student achievement.
For a more in-depth discussion of experimental research, refer to the publication Identifying and Implementing Educational Practices Supported by Rigorous Evidence: A User FriendlyGuide, recently released by the U.S. Department of Education’s Institute of Education Sciences. The publication can be viewed on the Web at
Data and Data-collection Strategies
TYPES OF DATA: QUANTITATIVE AND QUALITATIVE
In quantitative research, the data are numbers and measurements; in qualitative research, the data are narrative descriptions and observations. Other differences are thatqualitative research occurs in more natural and less controlled research settings than does quantitative research, and qualitative research often uses special methods to collect data, such as case study and ethnography. These methods reflect the philosophy of qualitative research, which emphasizes in-depth descriptions of persons, behaviors and contexts.
With regard to research designs, correlational,experimental and quasi-experimental designs usually collect quantitative data. Simple descriptive and comparative descriptive designs collect either type of data. When both quantitative and qualitative data are collected in the same study, the approach is called mixed methods.
DATA-COLLECTION STRATEGIES: LONGITUDINAL AND CROSS-SECTIONAL
Longitudinal and cross-sectional are data-collectionstrategies that can be used with either descriptive or experimental research designs.
Example of a descriptive longitudinal research study:
A researcher studies the relationship between the average class size that each student experienced in grade 2 and each student’s achievement in grades 2, 4, and 6. The purpose is to determine whether the relationship between class size and achievement remains...