Final answer:
The statement that a variable with the properties of an interval variable and a true zero is a ratio level variable is true. Ratio scale data allows for meaningful differences and ratios to be calculated, unlike interval scale data which lacks a true zero.
Step-by-step explanation:
A variable that has all the properties of an interval variable, but also has a true zero, is indeed a ratio level variable. This statement is true. Ratio scale data has meaningful differences between values and allows for the calculation of ratios because it has a true zero point. An example is a set of multiple choice exam scores such as 80, 68, 20, and 92, which can be ordered, differences between scores are meaningful, and ratios like '80 is four times 20' can be calculated.
Unlike interval scale data, which is similar to ordinal data in that it has a definite ordering, ratio scale data has a starting point or true zero, allowing for these comparisons of magnitude. Knowing that a score of 80 is four times the score of 20 is possible only because 0 represents the absence of what is being measured, which is not the case with interval scale data.
Understanding concepts such as proportions, unit rates, and unit scales also helps in identifying ratio level variables. A proportion involves equivalent ratios, a unit rate compares two measurements with one having a value of 1, and a unit scale compares actual dimensions to those of a model or drawing without requiring that either value be 1.