What is an experiment?
Experiments are scientific procedures that can test a prediction (hypothesis) by manipulating a factor(s) of interest and holding everything else constant (under control).
For example, in a laboratory simulation study investigating effects of fatigue on railroad engineer performance, it is possible to change hours of sleep the previous night (e.g. 4 vs. 8 hours) and observe the number of signals a participant misses.
What are some advantages of using experiments?
The advantage of an experiment is that it can provide evidence of a cause and effect relationship. This cannot be done using any other methods. For example, if an experiment participants who got 4 hours of sleep missed more signals than participants who got 8 hours, results would support the conclusion that the effect was due to sleep duration (assuming all other factors were held constant).
Experiments can be used to study operator performance as a function of multiple conditions such as weather, fatigue, noise, etc. Experiments can also be used to evaluate or compare technologies such as different versions of rail cab designs.
Settings for conducting experiments
Think of lab coats and beakers when hearing the word "experiment?" Experiments can be conducted either the complexity of real world settings, or in the controlled circumstances of a laboratory. Experiments can be used to learn about a wide range of things from simple (e.g. bacteria growing in a petri dish), to complex (e.g., human behaviors while operating a train). Real world settings do not have the control over the situation, or protection from possible harm, that is needed to conduct an experiment. Common practice is to conduct such experiments in a simulator, which serves as a kind of laboratory.