1. Why do we do experiments?
To test ideas, beliefs, hypotheses, claims of others etc. In principle, no appeals to prior or higher authorities are acceptable in scientific investigations. In practise, of course, because we try and test one idea at a time, we assume that the established body of scientific knowledge regarding all other questions is acceptable. Provisionally. We start from a position of scepticism. This can help us to determine whether a hypothesis is amenable to further substantiation or refutation.
Some example hypotheses:
1) Drinking alcohol impairs pronunciation.
2) During speech, articulators move from one position to another in the way that requires least effort.
Often, we try and test ideas that seem intuitively obvious, because sometimes the obvious is not true.
2. Some characteristics of experiments
a) Experiments make controlled comparisons between different states of affairs. For example, one variable v1 (the dependent variable) is observed as another variable v2 (the independent variable) is deliberately altered, to try to determine whether changes in v2 appear to be related to (and, we believe, give rise to) changes in v1. For example, v2 could be quantity of alcohol consumed and v1 word pronunciation error rate.
b) Because an effect might have multiple interacting causes, we begin by attempting to isolate and manipulate factors individually, by holding all other variables constant. For example, when using human subjects, we might regard it as important to use a group that is homogenous with regard to age group, sex, social background, language, dialect, religion, level of education, whether or not they are trained in phonetics/linguistics/psychology, time of day (people get more tired as the evening passes), whether they smoke, use drugs, are on medication etc.
c) The variables studied are quantitative i.e. they can be counts or measurements. (Yes/no and multiple-choice response formats are a kind of counting.)
d) Robustness of results. A single set of measurements may be faulty (as a result of inadvertent error), or even if accurate, unrepresentative of other situations, and hence not a suitable basis on which to make general statements. One swallow does not make a summer. Additionally, natural phenomena are often inherently variable, to a certain degree. We would like to understand and account for that variability, rather than wish it away. To avoid the fragility of single observations, experiments are usually repeated many times e.g. through the use of several subjects, re-runs of the procedure, reproducing the work of other experimenters to confirm or refute their conclusions. Because of multiple trials, a lot of data may be collected germane to a single quesion. Statistical techniques are employed to determine the significance of the mass of data to the question under consideration.
e) In reports of experiments, there should be less need for extended discussion of the pros and cons of different viewpoints and opinions, as in most linguistics papers. Any claims advanced should stand or fall by the report of the conduct of the experiment and the analysis of results. Speculations may be reported as a basis for future work.