223
7.3.5.5 Public scale construction and application, and calibration
The local values obtained by the test are not broadly useful other than when using
that specific set of items I m , as the relationship between the local values for this set
and the local values for a different set of items is not generally known. Whenever
the comparability of results may remain local to the context where the same instrument is used (e.g., within a single teacher’s classroom), this may not be a problem,
but a further step would be needed to equip them for public usage, through the definition of a public scale of RCA against which different RCA tests could be calibrated (see Fig. 7.8). There are several ways to do this that are common in educational
measurement. Here we describe two common approaches.
Fig. 7.19 A reading comprehension ability construct map
7.3 A structural model of direct measurement
7.3.5.5 Public scale construction and application, and calibration
The local values obtained by the test are not broadly useful other than when using
that specific set of items I m , as the relationship between the local values for this set
and the local values for a different set of items is not generally known. Whenever
the comparability of results may remain local to the context where the same instrument is used (e.g., within a single teacher’s classroom), this may not be a problem,
but a further step would be needed to equip them for public usage, through the definition of a public scale of RCA against which different RCA tests could be calibrated (see Fig. 7.8). There are several ways to do this that are common in educational
measurement. Here we describe two common approaches.
Fig. 7.19 A reading comprehension ability construct map
7.3 A structural model of direct measurement