Number lines, counting, and measuring in arithmetic education

Over the course of two days spent at a meeting on mathematics education, a question started to form in my mind, one I don’t know how to answer, and to which there may be no answer. I’d like to try to formulate what’s on my mind in writing, and see if it’s just nonsense, a curiosity, some old debate that’s been long since resolved, issues too complex to try to use in elementary education, or something we might actually want to try to do something about.

The question stems from my long experience in measurement. It is one of the basic principles of the field that counting and measuring are different things (see the list of publications on this, below). Counts don’t behave like measures unless the things being counted are units of measurement established as equal ratios or intervals that remain invariant independent of the local particulars of the sample and instrument.

Plainly, if you count two groups of small and large rocks or oranges, the two groups can have the same number of things and the group with the larger things will have more rock or orange than the group with the smaller things. But the association of counting numbers and arithmetic operations with number lines insinuates and reinforces to the point of automatic intuition the false idea that numbers always represent quantity. I know that number lines are supposed to represent an abstract continuum but I think it must be nearly impossible for children to not assume that the number line is basically a kind of ruler, a real physical thing that behaves much like a row of same size wooden blocks laid end to end.

This could be completely irrelevant if the distinction between “How many?” and “How much?” is intensively taught and drilled into kids. Somehow I think it isn’t, though. And here’s where I get to the first part of my real question. Might not the universal, early, and continuous reinforcement of this simplistic equating of number and quantity have a lot to do with the equally simplistic assumption that all numeric data and statistical analysis is somehow quantitative? We count rocks or fish or sticks and call the resulting numbers quantities, and so we do the same thing when we count correct answers or ratings of “Strongly Agree.”

Though that counting is a natural and obvious point from which to begin studying whether something is quantitatively measurable, there are no defined units of measurement in the ordinal data gathered up from tests and surveys. The difference between any two adjacent scores varies depending on which two adjacent scores are compared. This has profound implications for the inferences we make and for our ability to think together as a field about our objects of investigation.

Over the last 30 years and more, we have become increasingly sensitized to the way our words prefigure our expectations and color our perceptions. This struggle to say what we mean and to not prejudicially exclude others from recognition as full human beings is admirable and good. But if that is so, why is it then that we nonetheless go on unjustifiably reducing the real characteristics of people’s abilities, health, performances, etc. to numbers that do not and cannot stand for quantitative amounts? Why do we keep on referring to counts as quantities? Why do we insist on referring to inconstant and locally dependent scores as measures? And why do we refuse to use the readily available methods we have at our disposal to create universally uniform measures that consistently represent the same unit amount always and everywhere?

It seems to me that the image of the number line as a kind of ruler is so indelibly impressed on us as a habit of thought that it is very difficult to relinquish it in favor of a more abstract model of number. Might it be important for us to begin to plant the seeds for more sophisticated understandings of number early in mathematics education? I’m going to wonder out loud about this to some of my math education colleagues…

Cooper, G., & Humphry, S. M. (2010). The ontological distinction between units and entities. Synthese, pp. DOI 10.1007/s11229-010-9832-1.

Wright, B. D. (1989). Rasch model from counting right answers: Raw scores as sufficient statistics. Rasch Measurement Transactions, 3(2), 62 [http://www.rasch.org/rmt/rmt32e.htm].

Wright, B. D. (1993). Thinking with raw scores. Rasch Measurement Transactions, 7(2), 299-300 [http://www.rasch.org/rmt/rmt72r.htm].

Wright, B. D. (1994, Autumn). Measuring and counting. Rasch Measurement Transactions, 8(3), 371 [http://www.rasch.org/rmt/rmt83c.htm].

Wright, B. D., & Linacre, J. M. (1989). Observations are always ordinal; measurements, however, must be interval. Archives of Physical Medicine and Rehabilitation, 70(12), 857-867 [http://www.rasch.org/memo44.htm].

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