The last metric scale is called ratio measurement scales. Ratio along with interval scales affords the most precise data. With both there are equal intervals or units between any two consecutive numbers.
The only difference between ratio and interval scales is the role of zero (0). In interval scales zero is artificial rather than real. IQ and standardized tests for performance assessment have a zero (0), but it is artificially created rather than real. In ratio scales, zero is real. It signifies the absence of the variable under study. An example is Number of Days Absent from School.
Ratio scaling is similar to interval scaling in terms of equivalent values between numbers. The only difference is that in ratio scales a zero (0) means something important. It means the absence of whatever the scale is measuring. This type of scaling is encountered more commonly in the physical sciences where there can really be “no” weight, time, height, water pressure, or wherever zero is real not artificially created.
Return from ratio measurement scales to variables and instruments.