Question Posted 02/15/18:
What is meaning of baseline diagnosis? What is the difference between VISCODE and VISCODE2?
Response posted 02/15/18 by Danielle:
The baseline diagnosis is the diagnosis at the baseline visit. Individuals are identified as normal, MCI or demented.

VISCODE is the code used for a particular visit. In ADNI1, this was easy to interpret as the codes corresponded to a particular month visit. In ADNIGO/2, this changed, so that the VISCODE was no longer easily interpreted. VISCODE2 translates the VISCODEs into a corresponding month visit for each individual.
Response posted 02/15/18 by Vandana:
Thank you for answer.
I have following question,
How do I know the 819 individuals enrolled in ADNI1 belong to NC / MCI / Ad?
Response posted 02/15/18 by Danielle:
The easiest place to find this information is in the ADNIMERGE file (Key tables merged together - available on the study data page). There is a variable for baseline diagnosis. You can use RID< 2000 to identify ADNI-1 participants. Alternatively, you can find the diagnosis information in the Diagnostic Summary file - for ADNI-1, use DXCURREN and VISCODE=="bl" to get the baseline diagnosis (refer to the data dictionary, also available for download on the same page for coding information).