15.2.1: Testability, Accuracy, and Precision

If a proposed hypothesis (a claim) cannot be tested even indirectly, it is not scientific. This point is expressed by saying that scientists highly value testability. For example, suppose someone suggests, “The current laws of chemistry will hold true only as long as the Devil continues to support them. After all, the Devil made the laws, and he can change them on a whim. Luckily he doesn't change his mind too often.” Now, what is a chemist to make of this extraordinary suggestion? Even if a chemist were interested in pursuing the suggestion further, there would be nothing to do. There is no way to test whether the Devil is or isn't the author of the laws of chemistry. Does the Devil show up on any scientific instrument, even indirectly? Therefore, the Devil theory is unscientific.

Scientists value accuracy and precision. An accurate measurement is one that agrees with the true state of things. A precise measurement is one of a group of measurements that agree with each other and cluster tightly together near their average. However, precision is valuable to science more than in the area of measurement. Precise terminology has helped propel science forward. Words can give a helpful push. How? There are two main ways. A bird may go by one name in the Southeastern United States but by a different name in Central America and by still a different name in Africa. Yet scientists the world over have a common Latin name for it. Thus, the use of precise terminology reduces miscommunication among scientists. Second, a precise claim is easier to test than an imprecise one. How do you test the imprecise claim that "Vitamin C is good for you"? It would be easier to run an experiment to check the more precise claim "Taking 400 milligrams of vitamin C per day will reduce the probability of getting a respiratory infection by fifty percent." If you can test a claim, you can do more with it scientifically. Testability is a scientific virtue, and precision is one path to testability.

Because the claims of social science are generally vaguer than the claims of physical science, social scientists have a tougher time establishing results. When a newspaper reports on biology by saying, "Vitamin C was shown not to help prevent respiratory infections," and when the paper reports on social science by saying, "Central America is more politically unstable than South America," we readers don't worry as much about "help prevent" as we do about "politically unstable." Behind this worry is our understanding that "help prevent" can readily be given an unproblematic operational definition, whereas "politically unstable" is more difficult to define operationally. That is, the operation the biologist performs to decide whether something helps prevent respiratory infections can be defined more precisely, and easily, and accurately than the operation to be performed to decide whether one country is more politically stable than another.

Although vagueness is usually bad and precision good in science, pseudoprecision is also to be avoided. Measuring a person's height to five decimal places would be ridiculous. The distance between two parallel mirrors can have that precision, but human height cannot, even though they are both lengths. Unfortunately, when newspaper and TV stories report some scientific result to us, they rarely tell us how the scientists defined their controversial terms. Information gets to the public by being created in science labs, then the information is published in scientific journals and other professional publications. Sometimes reporters of newspapers and magazines pick up the information here, then try to say it more simply for the nonscientists. Or perhaps the reporters notice it in the journal, then telephone the scientist to ask for it to be explained to them more simply. Then they publish on their webpage or on the air or in their newspaper, and in this way the average citizens learns about it. Hardly any ordinary citizen checks things out for themselves.