Comparability over time [stasis-flux issue]
A person identity processes followed through time constitute changing features according to the flux of ongoing experiences and the reappraisal of past experiences. Identity processes are not static and a person's identity is a matter of continuity rather than sameness, where continuity will at times reflect major biographical transitions. In living in the world, the person encounters numerous agents, some of them being people and institutions already known, and some others being previously unknown but who come to have great significance. In practice, the nexus of other agents that is significant to the person changes over time. An appropriate identity instrument at a subsequent phase of a person's biography needs to encompass the elaborations in identity processes that ensue in time, including relevant additional entities and discourses. An identity instrument for a later phase will be an elaboration of the earlier one.
When the person's identity instrument at the later phase differs from that at the earlier phase, it would seem that comparability over time is lost. However, this is not the case, because the internal standardisation procedures for identity parameters proceed for each instance. While particular qualitative features differ, these are taken into account by way of internal standardisation, so that the assessed quantitative parameters remain standardised to the same scalar properties. No assumption of 'item' stasis (as in the fixed items of a psychometric scale) is made, and flux is incorporated naturally within the practical procedures of the ISA conceptual framework.