44
Euclidean basis of this assumption is not sufficient as such for maintaining the constraint: this will pave the way for a further analysis about measurability.
3.2 The quality of measurement and its results
In Chap. 2 we introduced the distinction between a measurement procedure and a
measurement process: the former is the description that specifies how the latter, i.e.,
the process, must be performed. Even if the specifications are exactly fulfilled, two
measurement processes implementing the same procedure on the same object may
produce different results. This calls for an explanation.
In principle, two situations might be obtained. The property with which the measuring instrument is designed to interact either:
• has changed, so that different measurement results may correctly report the fact
that the object under measurement modified its state in the interval between the
interactions, or
• has not changed, but the behavior of the measuring instrument has been affected
by changes in the state of the environment or of the measuring instrument itself,
so that different measurement results incorrectly report a difference that is not
related to the measurand.
1
From the perspective of measurement as such, the first case is not problematic: the
property under measurement may actually change as the result of its dependence on
other properties, of the object or the environment. We call any property whose
changes produce a change in the measured property an affecting property. For example, if the measured property is the length of an iron rod, then, due to thermal expansion, an example of an affecting property is the temperature of the rod. If the
measured property is the reading comprehension ability of a student, an example of
an affecting property might be the intensity of distracting noises from the environment (insofar as such noise could negatively affect the student’s ability to comprehend a text they are attempting to read). On the other hand, there can be properties
other than the measurand which alter the behavior of the measuring instrument and
therefore generate the second case; these are called influence properties (JCGM,
2012: 2:52). In the example of the measurement of the thickness of a rod by means
of a caliper, an example of an influence property is the parallelism of the jaws,
1 Eran Tal (2019) builds upon this distinction and argues that “due to the possibility of systematic
error, the choice between [these two situations] is underdetermined in principle by any possible
evidence”: we do not further develop his argument here. Moreover, there is a third case: whether
the individual property did change or not, what may change over time is the definition of the general property of which the individual property is an instance, thus possibly making the measuring
instrument inadequate. While this is (now) unusual for physical properties, this situation is (still)
not uncommon in the human sciences, as for example for nursing ability, the very definition of
which depends on the cultural context and therefore changes over places and times. We discuss the
problem of the existence and identification of general properties in Sect. 6.6.
3 Technical and cultural contexts for measurement systems
Euclidean basis of this assumption is not sufficient as such for maintaining the constraint: this will pave the way for a further analysis about measurability.
3.2 The quality of measurement and its results
In Chap. 2 we introduced the distinction between a measurement procedure and a
measurement process: the former is the description that specifies how the latter, i.e.,
the process, must be performed. Even if the specifications are exactly fulfilled, two
measurement processes implementing the same procedure on the same object may
produce different results. This calls for an explanation.
In principle, two situations might be obtained. The property with which the measuring instrument is designed to interact either:
• has changed, so that different measurement results may correctly report the fact
that the object under measurement modified its state in the interval between the
interactions, or
• has not changed, but the behavior of the measuring instrument has been affected
by changes in the state of the environment or of the measuring instrument itself,
so that different measurement results incorrectly report a difference that is not
related to the measurand.
1
From the perspective of measurement as such, the first case is not problematic: the
property under measurement may actually change as the result of its dependence on
other properties, of the object or the environment. We call any property whose
changes produce a change in the measured property an affecting property. For example, if the measured property is the length of an iron rod, then, due to thermal expansion, an example of an affecting property is the temperature of the rod. If the
measured property is the reading comprehension ability of a student, an example of
an affecting property might be the intensity of distracting noises from the environment (insofar as such noise could negatively affect the student’s ability to comprehend a text they are attempting to read). On the other hand, there can be properties
other than the measurand which alter the behavior of the measuring instrument and
therefore generate the second case; these are called influence properties (JCGM,
2012: 2:52). In the example of the measurement of the thickness of a rod by means
of a caliper, an example of an influence property is the parallelism of the jaws,
1 Eran Tal (2019) builds upon this distinction and argues that “due to the possibility of systematic
error, the choice between [these two situations] is underdetermined in principle by any possible
evidence”: we do not further develop his argument here. Moreover, there is a third case: whether
the individual property did change or not, what may change over time is the definition of the general property of which the individual property is an instance, thus possibly making the measuring
instrument inadequate. While this is (now) unusual for physical properties, this situation is (still)
not uncommon in the human sciences, as for example for nursing ability, the very definition of
which depends on the cultural context and therefore changes over places and times. We discuss the
problem of the existence and identification of general properties in Sect. 6.6.
3 Technical and cultural contexts for measurement systems