In environmental science, experimental design is an extremely important part of the scientific method. When a scientist seeks to prove or disprove a hypothesis, he or she must carefully design the experiment so that it tests only one thing, or variable. If the scientist doesn’t design the experiment carefully around that one variable, the results may be confusing.

The two main types of experiments scientists use to test their hypotheses are

  • Natural experiments: Natural experiments are basically just observations of things that have already happened or that already exist. In these experiments, the scientist records what he or she observes without changing the various factors. This type of experiment is very common in environmental science when scientists collect information about an ecosystem or the environment.

  • Manipulative experiments: Other experiments are manipulative experiments, in which a scientist controls some conditions and changes other conditions to test the hypothesis. Sometimes manipulative experiments can occur in nature, but they’re easier to regulate when they occur in a laboratory setting.

    Most manipulative experiments have both a control group and a manipulated group. For example, if a scientist were testing for the danger of a certain chemical in mice, the scientist would set up a control group of mice that weren’t exposed to the chemical and a manipulated group of mice that were exposed to the chemical.

    By setting up both groups, the scientist can observe any changes that occur only in the manipulated group and be confident that those changes were the result of the chemical exposure.

    When designing manipulative experiments, scientists have to be careful to avoid bias. Bias occurs when scientists have some preconceived ideas or preferences concerning what they are testing. These ideas may influence how they set up the experiment, how they collect the data, and how they interpret the data.

    To avoid bias, an environmental scientist can set up a blind experiment, in which other scientists set up a control group and a manipulated group and don’t inform the scientist who’s actually observing the experiment which one is which.