Page 222 - Let them speak Towards a patient reported outcome measure set for

Chapter 8
Content validity
Content validity is a crucial measurement property of a PROM, reflecting
how well its items capture the construct being measured (46). It includes
three components: relevance (i.e., whether items reflect the construct),
comprehensiveness (i.e., whether all key aspects of the construct are
covered), and comprehensibility (i.e., whether items are understood by
patients and proxies) (47). Given the heterogeneity of GID, assessing the
relevance, comprehensiveness, and comprehensibility of PROM items
for the whole GID population is essential. Caregivers of individuals with
fragile X syndrome have reported that existing instruments often include
irrelevant or developmentally inappropriate items, causing frustration
during completion (11). Moreover, some items may be appropriate for
individuals with higher intellectual functioning but unsuitable for those with
severe or profound ID. For instance, while social functioning/participation
is part of the core PROM set, this construct manifests differently across
levels of intellectual functioning. Individuals with higher intellectual abilities
may form and maintain friendships, whereas this is often not possible for
those with severe or profound ID. Moreover, these individuals often do not
(yet) have a need for friendships, but rather a need for a safe and trusting
relationship with their primary caregiver. As such, items may need to be
added or removed to fully capture social functioning/participation for
individuals with severe to profound ID.
It is also essential to assess whether individuals with GID, particularly those
with ID, and their caregivers understand the items. Items that are easily
understood by individuals with normal intellectual functioning may not be
clear to those with ID. It is also important to determine from which level of ID
individuals can reliably self-report and for which individuals adaptations are
needed to improve comprehensibility. This may result in separate versions
of the core PROM set for individuals with ID and for those without ID.
Content validity should be assessed in line with the COSMIN (COnsensus-
based Standards for the selection of health Measurement INstruments)
guidelines (48). At the Amsterdam UMC/Emma Children’s Hospital, initial
efforts are already being made to simplify items within the PROMIS item
220