Dear experts,
After looking at the REGISTRY file, I see that many participants went through screening without any indication of issues, but have no follow-up data - this includes even absence of a baseline appointment. Am I missing information? Or how do I find out why a participant may have passed screening but then failed to have any further appointments? Thank you.
We recommend considering the differences between the diagnosis assigned at the screening visit and the diagnosis at the baseline visit. In all phases of ADNI, a subset of the initial information was collected during the screening visit. Once an individual was deemed eligible for the study, they returned for the 'baseline' visit, where a diagnosis was provided. The Clinical Core suggests using the diagnosis at baseline because it is based on a more comprehensive evaluation of the individual. Since the images were acquired during the screening visit, the diagnosis linked to them in the IDA corresponds to the screening visit, contributing to some discrepancies.
For individuals with initial images not found in the DXSUM file, the majority are either screen failures or individuals who withdrew from the study. You can find information about them in the REGISTRY file. If the VISCODE is 'f' and the individual is an ADNI-1 subject, it indicates a screening failure. Another informative variable is RGCONDCT, which specifies whether or not the visit was conducted.
