Hi Krina,
The Bayley is a discriminative measure as each administration results in scores based on comparisons to normative values (the normal sample distributed on a bell curve). Therefore, you are “discriminating” the child’s performance from that of typically developing peers.
Evaluative measures are designed to “evaluate” a child’s performance over time (or from at least 1 administration to another). These scores are not plotted against normative data on a bell curve. The initial administration of the test is often a baseline assessment, which serves as a comparison to future administrations. Therefore, you can evaluate change over time. Values such as the MDC and MCID help us interpret the meaningfulness of the child’s change. Examples of evaluative measures are the GMFM and the TUG test.
The Bayley is not designed to evaluate a child’s performance over time (comparison of scores from multiple administrations) as each administration results in scores derived from a new table of normative data. Therefore, at each administration the child is compared to a new normative sample, not themselves. The Bayley is not capable of generating change scores like the GMFM-66.
We hope this explanation is helpful!
Helen and Jessica