Ratio Scale
The ratio scale provides a cardinal and an ordinal form of measurement. It has
the three desirable properties covered so far, namely classification, magnitude
and equal intervals. It is distinguished by the fourth significant quality it
possesses, absolute zero. For example, an item that weighs nought (0)
kilograms has no weight at all (as happen in outer space). Most measurements
used in the physical sciences, such as weight, volume and speed, use the ratio
scale.
A ratio scale incorporates another quality that is true to its name. Where items
have different measurements the ratio of the measurements reflects the ration
of the property that is being measured. To illustrate this, the Kelvin scale for
measuring temperature is a ratio scale. Thus on the Kelvin scale 40 degrees is
twice as hot as 20 degrees. By contrast, on the Celsius scale, 60 degrees is not
three times as hot as 20 degrees. It is simply 40 degrees hotter (60
°
-20
°
= 40
°)
Summary
These scales and their properties are summarised in the following table:
Classification
Magnitude
Equal Intervals
Absolute Zero
Nominal Scale
Yes
No
No
No
Ordinal Scale
Yes
Yes
No
No
Interval Scale
Yes
Yes
Yes
No
Ratio Scale
Yes
Yes
Yes
Yes
Figure 12.1 Summary of Measurement Scales
Scales and Popular Sayings
Some popular sayings are best explained by reference to these forms of
measurement. On the surface the proverb “half a key opens no door” and its
close relative “a miss is as good as a mile” are in conflict with the proverb
“half a loaf is better than no bread”. Yet they all make sense by reference to
the appropriate measuring scale. “Half a key opens no door” is apposite to
items that are measured on the nominal scale where you are or you are not, or
you are in or you are out. As the popular saying goes “there is no half
measure”. By contrast the nostrum that “half a loaf is better than no bread” is
appropriate for items that are measured on the interval or ratio scale.
Reference to the interval and ratio scales can also resolve an apparent
contradiction between two sayings. According to popular wisdom if a thing is
worth doing it is worth doing properly. In other words, if it is a good thing you
might as well have as much as you can acquire. Yet according to GK
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