Geography Reference
In-Depth Information
is a multiplicative factor warmer than the other. (Three times -20 is -60—a clearly wrong result.) The
use of multiplication (*) and division (/) with interval data is not completely ruled out, however. As
long as the answers are understood to be in the context of the arbitrary zero, you can make limited
use of * and /. For example, if the morning temperature were 20ºF and the afternoon 60ºF, you could
say that the mean temperature was 40 ºF ((20 + 60)/2) = 40.
Ratio—A set of ratio-scale data is like an interval-scale data set, with the additional proviso of a non-
arbitrary zero point. The simplest example might be measured distances. A ruler has an absolute
zero and a unit value of 1 inch. I can say both that, if desk A is 30 inches long and desk B is 45 inches
long, desk B is 15 inches longer than desk A, and also that desk B is 1.5 times as long as desk A.
With ratio data you may use any comparison or arithmetic operators (=, < >, <, <=, >=, >, +, -, *, /,
and exponential (^ or **)) plus a whole batch of functions, such as square root. Of course, you must
be careful to know the limits and characteristics of your data. You may not, for example, take the
logarithm of a negative number. And when taking the cosine of 450º you must understand what that
means.
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