The Science Experiment

A science experiment is a set of actions and observations, performed in the context of solving a particular problem or question, to support or falsify a hypothesis or research concerning phenomena. The experiment is a cornerstone in the empirical approach to acquiring deeper knowledge about the physical world.

Science experiments conducted in accord with the scientific method have several features in common. An experiment is usually conducted to test a hypothesis about the role of one variable (the independent variable) on another the (dependent variable). There are two primary concerns in designing an experiment:

* To make certain, as far as possible, that the independent variable is the only factor that varies systematically in the experiment; in other words, that the experiment is appropriately controlled - that confounding variables are eliminated
* To make certain, as far as possible, that the dependent variable truly reflects the phenomenon under study (a question of validity) and that the variable can be measured accurately (i.e., that various types of experimental error, such as measurement error can be eliminated)

In a pure application of the scientific method, hypotheses are tested by critical experiments: ones that can falsify the hypothesis in the case of a non-result (i.e., an experiment showing that the independent variable did not affect the dependent variable as predicted). Such pure applications are rare, however, in part because a result can sometimes be challenged on the basis that an experiment was not sufficiently controlled, that the dependent variable was not valid, or that various forms of error compromised the experiment. The scientific method, as a result, builds in the need for reproducibility (usually termed replication) and convergent evidence

The design of a science experiment attempts to balance the requirements and limitations of the field of science in which one works so that the experiment can provide the best conclusion about the hypothesis being tested.

In some sciences, such as physics and chemistry, it is relatively easy to meet the requirements that all measurements be made objectively, and that all conditions can be kept controlled across experimental trials. On the other hand, in other cases such as biology, and medicine, it is often hard to ensure that the conditions of an experiment are performed consistently; and in the social sciences, it may even be difficult to determine a method for measuring the outcomes of an experiment in an objective manner.

For this reason, sciences such as physics and several other fields of natural science are sometimes informally referred to as “hard sciences”, while social sciences are sometimes informally referred to as “soft sciences”; in an attempt to capture the idea that objective measurements are often far easier in the former, and far more difficult in the latter.

In addition, in the social sciences, the requirement for a “controlled situation” may actually work against the utility of the hypothesis in a more general situation. When the desire is to test a hypothesis that works “in general”, an experiment may have a great deal of internal validity, in the sense that it is valid in a highly controlled situation, while at the same time lack external validity when the results of the experiment are applied to a real world situation. One of the reasons why this may happen is the Hawthorne effect; another is that partial equilibrium effects may not persist in general equilibrium.

As a result of these considerations, experimental design in the “hard” sciences tends to focus on the elimination of extraneous effects, while experimental design in the “soft” sciences focuses more on the problems of external validity, often through the use of statistical methods. Occasionally events occur naturally from which scientific evidence can be drawn, which is the basis for natural experiments. In such cases the problem of the scientist is to evaluate the natural “design”.