Sunday, April 17, 2011

Hypothesis Testing

The scientific method has provided us with a means of understanding the universe and that which goes on within it. Hypothesis testing is the fundamental basis of the scientific method.  Hypothesis testing involves several steps: forming a hypothesis, devising an experiment to prospectively test that hypothesis, executing that experiment, and then determining whether the experimental results lead us to reject that hypothesis as applied to the specific conditions of the experiment. A hypothesis cannot be proven to be correct; we can attempt only to disprove it under different experimental conditions.  When a hypothesis has withstood repeated experimental attempts to disprove it, it becomes generally accepted.  A collection of one or more such well established hypotheses taken together with the supporting experimental evidence constitute a theory – a well established body of information that accounts for a range of phenomena.  Examples of such theories include Newtonian mechanics, the theory of evolution, etc. 

However, it has often been found that even well established hypotheses, and theories, may require modification when applied to conditions beyond the conditions under which they have been previously tested experimentally. For example, Newtonian mechanics predict with remarkable precision the motion of macroscopic objects which move with relative speeds which are very slow compared to the speed of  light.  However, for very small objects – on an atomic scale – Newtonian mechanics completely breaks down.  Quantum theory was developed for describing motion of very small particles.  Similarly, Newtonian mechanics breaks down as well for objects that are moving with relative velocities comparable to the speed of light.  The theory of relativity was developed by Albert Einstein to account for the behavior of objects moving with relative velocities comparable to the speed of light.  We now know that Newtonian mechanics is an approximation, a remarkably precise approximation, to the laws of motion for objects that are sufficiently large and move sufficiently slowly with respect to each other. 

Hypothesis testing is an extraordinarily powerful tool for knowing the world around us and within us and for making decisions.  Outside of purely scientific endeavors (and sometimes there as well) it is inadequately employed (see, for example, my recent post as to how hypothesis testing ought be used in developing a health care system).   We are too frequently guided by untested doctrine rather than by tested hypotheses.

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