Hi,
In the 'DXSUM_PDXCONV_ADNIALL.csv' file column attribute 'Diagnosis', whether ‘3=dementia’ is equivalent to '3=AD’. In the 'ADNIMERGE.csv' file column attribute 'DX', whether 'dementia' is equivalent to 'AD'.
Please refer to this response to a previous Ask the Experts question: http://adni.loni.usc.edu/support/experts-knowledge-base/question/?QID=209