How to Measure Mind?

The title of this booklet, ‘Mind Measuring Mind’, reflects a basic problem in psychology: Humans are taking measurements on humans. Not always of other humans, one can also do measurements on oneself. In fact that is a method often used in psychology, named ‘self-report’. Before we can concern ourselves with the gamut of measurement in psychology, there are some basic and general matters on measurement we have to think about.

What is measurement (in psychology)?

In psychology, we think up a concept or an idea, and devise something to measure it with. One often encounters the term ‘construct’ instead of ‘concept’, in the context of measurement. Here we will stick to using the term ‘concept’, and will not dive into the differences between concept and construct. For now the term concept suffices, and refers to the general idea of something in our surrounding that we would like to know a bit more of, e.g. by performing measurements on it.

Where does such a ‘concept’ originate from? Well, we think it up. For example, there has been a moment in the history of psychology when someone got the idea that people seem to be able to cope with several challenges, be they mental or behavioural. This ability has been termed ‘intelligence’. Next, one may want to compare people on this new concept, e.g. by asking them questions to answer, or having them puzzles to solve etc. Such activities have led do the development of IQ-tests, and IQ is now the measure of ‘intelligence’. I know I will not be doing historians of intelligence a favour by this extremely simplistic account, but for now it serves a purpose.

Concepts like intelligence, extraversion, self-efficacy, psychopathy, neuroticism, (this could be a very long list), etc. are well known concepts in psychology, and are typically assessed using a standardised set of questions or exercises. It’s like the psychologist can read off an instrument, often a standardised questionnaire, to find a number that then quantifies the concept under study. To illustrate how difficult this is, take intelligence as an example again. The IQ-test produces a number. If your IQ is 100 you’re exactly on average, if it is below 70 you are seriously challenged, if it’s above 130 you’re very bright. But it’s not that simple. There has been, and still is, a debate going on about the nature of intelligence and the worth of a measuring instrument like the IQ-test. What exactly is ‘intelligence’, and does it cover all aspects of what we may want to call ‘intelligent’ behaviour? The debate has been going on for over a century, and it may continue for quite some time (if it will ever end).

How do others do their measurement? In physics for example, one can read off the electrical potential difference using a specific instrument, a Volt-meter, and you immediately know the voltage, expressed in Volt. In psychology we do not have those instruments. Take IQ again, the number of the average IQ value, 100, does not even carry a unit (like Volt) to identify it with. It’s just 100. The extraversion scale is more difficult, there may not even be agreement on how to exactly measure this concept. The number that comes out of the measurement does not carry a unit, and is converted into a category like being ‘more or less’ extraverted, or introverted (the opposite).

So all measurement start with an idea or concept that some people find important enough to agree about, and to provide some standard for. In psychology it often serves to study differences between people, or to study the way people perceive the world (see Figure 8). In the former case people are the very object of interest, in the latter people can be used as a measurement instrument to study properties of objects, products, or other people in the world. Examples of ‘analytic’ judgements by people are the loudness of a tone, the quality of an odour, the intensity of a hunger pang or the trustworthiness one may attribute to specific person. ‘Hedonic’ properties by people refer to judgements of liking, preference or sympathy of whatever it is that can be assessed. Note that this can also be judgements about other people almost like they are just objects in the world.

Another set of measurements concerns psychological properties of people, like the above mentioned intelligence or extraversion. These are measurements for which a measurement device is developed, that we decide (or hope) does indeed measure the concept (e.g. intelligence or extraversion) we’re interested in.

Examples of fields in psychology that concern themselves mainly with measurements of people are Personality Psychology and Clinical Psychology. Fields studying mainly measurements by people are Psychophysics, Perception Psychology and Social Psychology.

Figure 8 Overview of different types of measurement in psychology (with examples from the text shown).

What exactly is measuring?

What are we really doing when are measuring something? Back to physics, and a very simple concept we all know: length or distance. One can measure the length of something with a ruler, and read off a number, typically in cm (one hundredth of a meter, Figure 9, left part). One can measure a distance to travel by reading off a number in Google Maps (in km (1000 m), Figure 9, middle part), or the odometer on your bike or in your car (Figure 9, right part). It’ll typically tell you a number of meters. There is a concept or an idea, length (or electric potential, intelligence, extraversion, or what have you), and to this you connect a number. Mostly a number, but it’s not uncommon to connect a word, often an adjective, that signals the outcome of a measurement of a concept. Some buildings may be characterised as ‘ugly’, your hedonic measurement of the aesthetic quality of a building may have this outcome.

Figure 9 Measuring lengths (left: adding a number (8 cm) to the length of a pencil; middle: adding a number (137 km) to the distance between Papenhoven, the Netherlands (where I live) and the University Hospital of Bonn, Germany; right: total distance a car has travelled, reading off the odometer, here showing 162,421 km).

Another measurement all of us make many times a day is shown in Figure 10. Yes, this is a measurement too. We have agreed on certain moments on the day by giving them a special name, say noon, midnight, 10 o’clock, or 15:34. Relative to the agreement we measure the moment on the day by looking at a clock. What this has to do with psychology? Not a lot, but these are examples. But by the way, durations, the difference between two points in time, are used in psychology a lot, as reaction times. Some EEG measurements may show a difference in processing speed between two conditions of 12 ms (milliseconds, 1/1000 of a second), or you may take 4.3 min to solve a puzzle as part of a cognitive test.

Figure 10 Clocks (left: analogue; right: digital), for time measurement.

What do these, and other measurements have in common? Well, they attribute a number to a concept. In Table 1 the above examples are summarised, listing the concept or idea and the number assigned by it through a measurement (using a measurement instrument). Note that many numbers also carry a unit. Such a unit refers to an agreed standard to which the number can be compared. This defines the meaning of the number. In length one knows what a meter (m) is, because there is an agreed standard to which we could compare what our rulers tells us. We never actually explicitly do this, as the ruler itself can act as such a standard, and is precise enough for most of our daily measurements. This also counts for your tape measure if you are a carpenter. Some measurements do not carry a unit, like IQ in Table 1, because there is no such agreed standard to compare the results of an IQ-test to.

You can see in Table 1 that there are a few lines that do not list a number, but another type of measurement result. In psychology we can find almost any type of outcome from some measurement instrument. In the examples in Table 1 you see ‘introvert’, as a measurement of the amount of someone being extraverted or not. Introversion is the opposite of extraversion and is related, by a measurement instrument, to certain behaviours a subject displays or thoughts a subject has. A simple test for ADHD is just to count how many of seven specific behaviours a person recognises in him/herself. In this case (in Table 1) only three, which led the psychologist conclude that the ADHD measurement results in a result ‘not ADHD’.

Table 1 Some concepts, and the number (some with unit) assigned to it by measurement, using a specific measurement instrument.

concept/idea	number	unit	measurement instrument
length of pencil	8	cm	ruler
length of road travel	137	km	google maps
total travel distance of car	162,421	km	odometer
time of day	15:34	hours and minutes	clock
processing speed	12	ms	EEG
time to solve a puzzle	4.3	min	stopwatch
IQ	117	-	IQ-test
(industrial) motion economy	12	Therbligs	workplace task analysis
intensity of sweetness of a drink	68	-	VAS (line scale ranging from ‘not sweet at all’ (0), to ‘extremely sweet’ (100))
grade on ‘introduction to psychology’ course	7.4	-	1st year BSc student exam on introduction to psychology (Dutch 0…10 grading system)
concept	result		measurement instrument
extraversion	introvert (not extravert)		introversion/extraversion questionnaire
ADHD	not ADHD (only 3 of the 7 behaviours present)		ADHD test
beauty of a building	ugly		choice of adjectives
ease of finding a book	agree		Likert item (“I could very easily find my books on this web site.”)
personality type	conscientious and agreeable		‘big 5’ questionnaire
psychopathy	schizophrenic		psychologist’s diagnosis
behavioural problem	anxiousness		psychologist’s diagnosis

So, what is a measurement? Very generally put, we perform a measurement on a concept, by assigning it a number, or a word (often an adjective). Very often it’s a number being assigned, but in psychology, a word (e.g. ‘ugly’, ‘schizophrenic’, ‘anxious’) may often be assigned to a concept (‘beauty’, ‘psychopathy’, ‘personality problem’, resp.) as well.