Over the centuries, humankind has spent a great deal of effort on measuring almost everything we encounter in our daily lives. Even the earliest societies attempted to express mass, length, and time in terms of numbers. Although the origin of some measurements is not definitively known, the tools used to measure mass, length, and time were among the earliest ones invented.

It was very natural that people focused on these measurements, as they were critical to everyday life. One of the first known attempts to measure length was the Egyptian cubit, developed around 3000 BC, which was based on the human body, one of the best tools then available to humanity. A “cubit” was the length of an arm from the elbow to the fingertips.

Similarly, early civilizations used what they had at their disposal to measure time, which was determined based on the regular movements of the sun. People used sundials, then candle clocks, water clocks, and sandglasses to measure time. As a result of the different methods used, the lengths of generally used time periods varied greatly from place to place – just as the units used to measure mass and length varied, too.

After the world became more interconnected, people needed a universal measure that could mean the same thing from one society to the next. In order to avoid confusion, an international standard unit of measurement, called the metric system, was created by France in 1790.

Latent constructs

During the last two centuries, the focus of measurement has shifted from observable objects to latent constructs such as traits, attitudes, and abilities. Latent constructs are based on certain theories. They can neither be observed nor measured directly. We attempt to measure them through some observable indicators, which are assumed to represent the underlying construct. For instance, the measurement of unobservable personal characteristics has challenged psychologists for centuries. Several approaches have been developed in an attempt to properly define and quantify these latent characteristics. Most of the current developments in these measurements are based on research into human sensitivity from classical psychophysics. In the 19th century, Ernst Weber, Gustav Fechner, and Herman von Helmholtz were some of the first scientists who attempted to measure human sensitivity to such sensory stimuli as lights, sounds, odors, tastes, and pressures.

Many social scientists have also been attempting to numerically identify some unobservable phenomena, such as ability, I.Q., and personality. In 1905, French psychologist Alfred Binet developed the Stanford-Binet IQ test to measure intelligence. Since then, other scholars have developed many tests for measuring intelligence. These tests are commonly used in educational and business settings.

Basic principle behind the successful measurement is to design a tool that can make it possible to obtain an accurate measure of what is intended to be measured. Despite the fact that all measurement instruments are subject to varying degrees of instrument error, psychometricians, who practice the science of measurement, and physical scientists have used different approaches to explain and reduce such errors. There are several differences between these two schools of measurement concepts. For instance, Stanley Smith Stevens (1946), an American psychologist, defined measurement as "the assignment of numerals to objects or events according to some rule." This definition is different than physical scientists’ definition which refers to the numerical estimation and expression of the magnitude of one quantity relative to another (Michell, 1997).

Conditions to measure the unobservable

Since measuring latent objects is more difficult than measuring observable phenomena, some conditions must be met before attempting to measure these unobservable things. First, they need to be identified based on a sound theory. An underlying theory should explain the causes and results of the variations of certain abstract phenomena, as well as the phenomena’s relationship with other constructs.

The second necessary condition for an object, either physical or latent, is that there is variation. Suppose that we are attempting to measure intelligence. If a group of individuals are found to be equally intelligent, there would be no need to measure and compare.

In addition to these two conditions, mathematical models are necessary to connect the theory and its observable indicators. Since these models assume a variable that can only be measured with error, our measurements may not reflect an exact quantity.

René Descartes (1644) claimed that, “If something exists, it exists in some amount. If it exists in some amount, then it is capable of being measured.” On the one hand, this philosophy teaches us that some things may exist which we have not yet measured. For instance, before Santorio Santorio invented the first thermometer, no one could express the temperature with a numerical value. However, temperature still existed, even before the existence of humankind. Therefore, humanity’s inability to measure something does not mean that it does not exist. On the other hand, a religious person can claim that there are some metaphysical objects believed to exist but which cannot be quantified. Therefore, the existence of something does not mean that it can be quantified – or at least, not by humankind.

There are reasons to be optimistic about the measurement of unobservable objects. First, most unobservable things have observable consequences. Thus, we can estimate many latent characteristics by observing the consequences on a person’s behavior. Let’s take personality as an example. An introverted person would tend to have a hard time being in front of a group of people. Such an observation can give us some idea about a person’s level of introversion. Measurements can focus on objective, behavioral reflections of a particular trait. This can be achieved by creating an instrument that is designed to measure the desired characteristic. The patient can be given a questionnaire and answer certain questions about the trait being measured. Answers based on the patient’s self-perception could be an indication of the degree of introversion. The person’s level of self-perception plays an important role.

Nevertheless, relying only on either our or someone else’s perceptions may not be a perfect form of measurement, as it is not possible for us to perceive everything about ourselves or the world around us. Our knowledge is very limited. If we cannot quantify an object either due to its hidden constructs or our inability to measure it, this does not mean that this object does not exist or it cannot be measured.

Though Adam may never be able to precisely answer his wife’s question about how much he loves her, it’s safe to say that his love exists, even if we can’t measure it.

References

• Descartes, R. Principia philosophiae, Amsterdam 1644. Pt, 2, 57-59.
• Michell, J. (1997). Quantitative science and the definition of measurement in psychology. British Journal of Psychology, 88, 355–383.
• Stevens, S. S. (1946). "On the Theory of Scales of Measurement". Science 103 (2684): 677–680.