Meaning and Intelligence
In a previous post, we explored the concept of the ‘meaning’ of a measurement. What exactly is it we are measuring? How does this relate to the quantity we actually want to know?
This led to a discussion in the last post of ‘direct’ and ‘indirect’ measurements, and the conclusion that almost all measurements today are of the indirect type. This has importance when we look more closely at errors, as indirect measurement of a quantity involves more actual measurements, each of which has its associated errors. These errors propagate through the reduction process in interesting ways, leading to interesting errors in the derived values. But that discussion must come after we have discussed some other topics.
In the post where we considered the ‘meaning’ of a measurement, we considered the apparently simple situation of measuring the length of a table. Things got progressively more complex as we thought through exactly what we were measuring and how it related to what we wanted for the ‘length’ of the table. However, what use is the length of the table by itself?
Direct and Indirect Measurement
In the previous post, direct and indirect measurements were measured, but these were not elaborated upon. Before we go any further, we should discuss these two concepts and why they are different.
When we use ‘direct’ measurement, we are measuring the desired quantity directly, i.e., we apply a measurement device directly to the particular quantity we wish to measure. For example, to measure the length of a table, as discussed in the previous post, we might place a tape measure on the tabletop, position the zero mark on the tape at one edge of the table, and read the distance on the tape at the other edge.
By contrast, ‘indirect’ measurement is where we measures something other than the desired quantity, then use a mathematical model to transform what we actually measured into an estimate of the desired quantity. Modern measurement technology has led to increasing amounts of indirect measurements, and direct measurement is becoming much less common.