Assessing the feasibility of linking Section G and Section GG measures of function in skilled nursing facilities

In skilled nursing facilities (SNFs), Section GG replaced Section G as the instrument for measuring function in 2023. To inform how previously validated scales and scores derived from Section G items might be re-produced from Section GG items, we examined key measurement assumptions in both instruments.

We identified 1,131,694 Minimum Data Set 3.0 assessments of unique persons with complete Sections GG and G between October 2018 and September 2023 across 2,200 SNFs in the Long-Term Care Data Cooperative. We examined: (i) assessment instructions, (ii) item-level Spearman's correlations, (iii) measures of fit and factor structure in confirmatory and exploratory factor analyses, and (iv) graded response item response theory parameters.

Several Section GG items were conceptually similar and highly correlated (ρ ≥ 0.7). After removing redundant items, a combined scale of both instruments was not unidimensional in confirmatory factor analyses (Comparative Fit Index = 0.753, Tucker-Lewis Index = 0.724, root-mean-square error of approximation = 0.153) and items from each instrument generally loaded onto separate but correlated factors (inter-factor correlation 0.735) in exploratory factor analyses. In item response theory analyses, Section GG items better captured independence while Section G items better captured dependence.

Sections GG and G measure related yet distinct constructs, emphasizing the need for caution when interpreting a sum of Section GG items as a reflection of underlying health in SNF patients. Scales and scores derived from Section G items cannot be presumed to be equivalent when derived from Section GG items, and further work is needed examining interchangeability.