In its conceptual framework for research on SCD in Alzheimer's disease (Jessen et al., 2014), the Subjective Cognitive Decline Initiative (SCD-I) working group highlighted the lack of common assessment procedures, which hampers the SCD construct and ability to compare research across studies and settings. To address this critical problem, we aim to link measures of subjective cognition using item response theory (IRT) across international aging studies. We combined item-level subjective cognitive data from the Alzheimer's Disease Neuroimaging Initiative (ADNI), Monongahela-Youghiogheny Health Aging Team (MYHAT), Indiana/Dartmouth Memory and Aging Study (IMAS/DMAS), and Harvard Aging Brain Study (HAB). We performed pre-statistical harmonization by assigning each item to one of eight cognitive domains by three independent raters. We dichotomized items due to limited or absent responses in some response categories and dropped items: (1) where fewer than 5 participants fell in a dichotomized response category; (2) that demonstrated a common factor loading qualitatively different from theoretical expectations; and (3) with arbitrarily large common factor loadings as evidence of local dependency. Multidimensional (bifactor) models consistent with IRT capturing a general SCD factor and specific cognitive domains were estimated using a robust maximum likelihood estimator with probit link function. We designated ADNI, with post-stratification weights to normalize the distribution by baseline diagnostic group, as the reference sample. Other studies were calibrated to ADNI by using parameter constraints on common items. Hypothetical item sets (short forms) were developed using simulation methods. We found good model fit for all ADNI items and subsequently fit bifactor models in HAB, followed by IMAS/DMAS, and MYHAT. We started with 333 items of which 233 were unique, and dropped 14 for sparse response coverage, 2 for suspected local dependence, and 51 for theory incongruous factor loading valence. We present study characteristics (Table) and item coverage for all available English language SCD-I studies (Figure). The figure displays how SCD-I working group studies and items will be linked together. The studies will be linked in the order presented on the figure from the top down, beginning with the Alzheimer's Disease Neuroimaging Initiative (ADNI, which is the reference sample). The black dots that look like horizontal bars are the items administered within a study. The black dots that are on top of the colored regions are unique items that haven't been calibrated by the studies listed above that study. The black dots that reside within a colored region are items that overlap with at least one study calibrated above it and form the link to calibrate the study's unique items. For example, the first pink bar shows a single item that is unique to the University of Pittsburgh Study/Monongahela-Youghiogheny Health Aging Team (Pitt-MYHAT) that is not yet calibrated in the Indiana/Dartmouth Memory and Aging Study (IMAS/DMAS), Harvard Aging Brain Study (HAB), or ADNI studies. The blue bar shows items administered in HAB that weren't in ADNI, but also administered in Pitt-MYHAT. The yellow band shows items unique to Vanderbilt Memory and Alzheimer's Center (VAMC) and not yet calibrated in the studies above it. Overall, the figure reveals very little item overlap across studies and no single item represented across all studies.