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Question Posted 01/10/22:
Dear ADNI,
first I would like to thank you for your work and effort. I hope I am contacting the correct core with my question - if my following question was already asked before and I have overseen it in the FAQ, I would like to apologize beforehand. Moreover, I already sent my questions to the ask the experts but I am not sure if these were received, thus I am contacting you again.

I am interested in the diagnoses (at the moment I am using the diagnoses summary file), more in detail if and when there is a change over time in the diagnosis of a participant, and several questions came up - maybe someone might help me with advices:
1) is there any information available about how long a participant already has a diagnosis - before the person participated in the study (e.g MCI or AD)? I only found history records regarding the family and medical history.

2) After the PDF document "inst_about_data-2" ADNI 2 coded the changes since the last measurement (however ADNI 1 and 3 coded the actual diagnosis at the measurement time point), and I encountered some ambiguities regarding this change coding in the DX summary file - how should I deal with this, in the following specific examples:

2.1) Reversion without explicit coding?: Some participants are coded at one measurement time point with a 5 (MCI to Dementia conversion) and after it at another measurement time point with a 2 (MCI stable) (or a 4 (NL to MCI conversion) and then a 1 (NL stable). Does it mean that this participant made a reversion although this is not coded (8: reversion Dementia to MCI)?
Or first they are coded as stable MCI (2), then at one measurement time point they are stable NL (1) and after it again stable MCI (2) and finally conversion MCI to Dementia (5).
2.2) Conversion without explicit coding?: For some participant after a 2 (stable MCI) a 3 is next coded (stable Dementia), does it mean this participant converted although there is no coded conversion like 5 conversion MCI to Dementia?
2.3) Different information in "baseline change summary info": In the table baseline change summary info with additional information it is for some participants noted, that they remain stable, however, they are code with a conversion in the summary diagnosis file?
2.4) Several conversion or reversions and stable in between: For some participants there are several following time points coded with a conversion (for example twice a 4 coded: NL to MCI conversion), sometimes they are stable in between (e.g: 5, 2, 5, 5, 3, 3). How should this be interpreted?
I understood in general, that if the participant's diagnosis changed since the last measurement a conversion was coded.

2.5) Quick changing diagnosis: For some participants the diagnoses changes from measurement to measurement (e.g stable NL (1), then conversion NL to MCI (4), then conversion MCI to Dementia (5) and then finally stable Dementia (3),) - the baseline change summary info doesn't give information, how should this be handled, as correct information?

Thus, in general my question is how to deal with the diagnosing over time that is not absolutely clear (however, in most of the cases it is clear, these are specifically picked cases in that we would like to know if we can include these participants - if more information is needed about specific cases, please let me know).

Many thanks in advance and kind regards,

Marthe Mieling
Response posted 01/10/22 by Danielle:
There was definitely some confusion in reporting the DXCHANGE variable - it seems as though sometimes, this was filled out as change since the baseline assessment, other times as change since the prior assessment, etc. I would recommend using the diagnosis suggested by the change variable (if reverted from MCI to NL then say the individual is NL, if progression from MCI to AD then say the individual is demented) and then create your own reversion/conversion variable. The ADNIMERGE file (ADNIMERGE - Key ADNI tables merged into one table [ADNI1,GO,2,3], which can be found on the Study Data page) has combined all of the diagnosis information from the various variables in the Diagnostic Summary file to give the participant's diagnosis at each visit, which might also be helpful.
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