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# Simple Experiments (page 2)

By Thomas Moorman
John Wiley & Sons, Inc.

### Experimental Design

Scientists use the term experimental design, or design of the experiment (or other investigation) to refer to different kinds of experiments. The design of the investigation is a most important part of doing good science. Professional scientists are always faced with the problems of the costs of an investigation, the amount of time they can devote to it, and other limits. You surely will be faced with similar limits as you do your investigation.

Many science projects displayed at science fairs cannot be seen as good investigations because the students simply did not put enough thought into their design. For example, you might see a project on growing plants that displays just one plant in each of two cups of soil. The experimenter's intention was to compare two different factors in the growth of the plants, such as a fertilizer ingredient or the color of the light. The big mistake in such limited investigations is the notion that the differences between just two such plants would be meaningful.

The fact is, the plants will differ anyway; no two plants are exactly alike. Therefore, the results are probably meaningless. The student doing such an investigation should consider investing much more thought, time, and materials in the project.

How many plants, or people, or animals should there be in such an investigation? For now, consider that 25 or more specimens should be used in each part of a controlled experiment for the results to be meaningful. Deciding about such numbers will get us into the study of what is called statistics. To some people, that term is a scary one, but it should not be. You are using statistics when you compare the scores of two teams in basketball, football, or other sports. You are using statistics when you look around a schoolroom and determine that there are more girls in the class than there are boys. You are using statistics when you judge that, at a certain age, girls on the average are taller than boys. Statistics simply means collecting and analyzing numerical data.

Statistics are a very important part of living as well as doing science, and you should learn how to be friendly with statistical concepts.

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