Forming Operational Definitions

In an experiment, it is often necessary to define one or more variables explicitly so that any researcher could measure or control the variable in exactly the same way. An operational definition describes how a particular variable is to be measured or how a term is to be defined. In this context, the term operational means “describing what to do.”

The gardener, for example, has to decide exactly how much lime to add to the soil. Can lime be added after the seeds are planted or only before planting? At what pH should no more lime be added to the soil? In this case, the gardener decided to add lime only before planting, and to add enough lime to make the pH equal in Groups 2 and 3.

Analyzing Data

The observations and measurements that are made in an experiment are called data. Scientists customarily record data in an orderly way. When an experiment is done, the researcher analyzes the data for trends or patterns, often by doing calculations or making graphs, to determine whether the results support the hypothesis.

For example, the gardener regularly measured and recorded data such as the soil moisture, daily sunlight, and pH of the soil. She found that the soil pH in Groups 2 and 3 started the same, but after two months the soil pH for Group 3 was a little higher than the soil pH for Group 2.

After harvesting the corn, the gardener recorded the numbers of ears of corn produced by each plant. She totaled the number of ears for each group. Her results were the following.

Group 1: 67 ears of corn

Group 2: 102 ears of corn

Group 3: 126 ears of corn

The overall trend was clear: The gardener's prediction was correct.

Drawing Conclusions

Based on whether the results confirm or refute the hypothesis, researchers make a final statement that summarizes the experiment. That final statement is called the conclusion. For example, the gardener's conclusion was, Adding lime to soil with a low pH will improve the production of corn plants.

Communicating Results

When an experiment has been completed, one or more events may follow. Researchers may repeat the experiment to verify the results. They may publish the experiment so that others can evaluate and replicate their procedures. They may compare their conclusion with the discoveries made by other scientists. And they may raise new questions that lead to new experiments. For example, Why does the pH level decrease over time when soil is treated with lime?

Evaluating and Revising

Scientists must be flexible about the conclusions drawn from an experiment. Further research may help confirm the results of the experiment or make it necessary to revise the initial conclusions. For example, a new experiment may show that lime can be effective only when certain microbes are present in the soil. Scientists continuously evaluate and revise experiments based on the findings in new research.