True experimental designs require random assignment. Control groups do not receive an intervention, and experimental groups receive an intervention. The basic components of a true experiment include a pretest, posttest, control group, and experimental group.

A positive control group is a control group that is not exposed to the experimental treatment but that is exposed to some other treatment that is known to produce the expected effect. For example, imagine that you wanted to know if some lettuce carried bacteria.

The control group (sometimes called a comparison group) is used in an experiment as a way to ensure that your experiment actually works. Your experimental group would be given the Gatorade and your control group would be given regular water. The conditions must be exactly the same for all members in the experiment.

Types of Experimental Design There are two basic types of research design: True experiments. Quasi-experiments.

Experimental Method

• Lab Experiment. Lab Experiment. A laboratory experiment is an experiment conducted under highly controlled conditions (not necessarily a laboratory), where accurate measurements are possible.
• Field Experiment. Field Experiment.
• Natural Experiment. Natural Experiment.

Different types of methods are used in research, which loosely fall into 1 of 2 categories. Experimental (Laboratory, Field & Natural) & Non experimental (correlations, observations, interviews, questionnaires and case studies). All the three types of experiments have characteristics in common.

Three Design Elements

• Manipulation (the ability to influence or direct the independent variable)
• Control (the ability to direct or influence important extraneous variables and study measurements)
• Randomization (unbiased [random] subject assignment to each group)

The three basic principles of statistical design of experiments are Control, Randomization and Repetition. When we say the design of an experiment (or experimental design), we refer to the manner in which these three principles are carried out.

In a controlled experiment, you must be able to:

• Systematically and precisely manipulate the independent variable(s).
• Precisely measure the dependent variable(s).
• Control any potential confounding variables.

Every science experiment should follow the basic principles of proper investigation so that the results presented at the end are seen as credible.

• Observation and Hypothesis.
• Prediction and Modeling.
• Testing and Error Estimation.
• Result Gathering and Presentation.
• Conclusions.
• Law Formation.

A good experimental design serves three purposes. Causation. It allows the experimenter to make causal inferences about the relationship between independent variables and a dependent variable . Control.

Terms in this set (6)

1. Identify the problem or question.
2. Form a hypothesis or solution to the problem.
3. Design the experiment to be used to test your hypothesis.
4. Carry out experiment.
5. Analyze data and observations.
6. State conclusion.

Experimental design is the process of planning a study to meet specified objectives. Planning an experiment properly is very important in order to ensure that the right type of data and a sufficient sample size and power are available to answer the research questions of interest as clearly and efficiently as possible.