Hi,

I have a question about the analysis of rates or percent changes.

I use data with available scans at baseline (TP1) and the 6-month (TP2), 12-month (TP3) and 24-month (TP4) follow-ups from ADNI dataset. An example of some of the data in the appropriate qdec table is given below:

fsid fsid-base years age weight diagnosis gender Glob_CDR NPI-Q_TotScr MMSE_TotScr FAQ_TotScr visit1_2_3_4

ADNI_sub1_sc ADNI_base1 0 81.3 y AD M x x x x sc

ADNI_sub1_m06 ADNI_base1 0.528767123 81.9 y AD M x x x x m06

ADNI_sub1_m12 ADNI_base1 1.030136986 82.4 y AD M x x x x m12

ADNI_sub1_m24 ADNI_base1 2.030136986 83.4 y AD M x x x x m24

ADNI_sub2_sc ADNI_base2 0 74 y AD F x x x x sc

ADNI_sub2_m06 ADNI_base2 0.501369863 74.5 y AD F x x x x m06

ADNI_sub2_m12 ADNI_base2 1.005479452 75 y AD F x x x x m12

ADNI_sub2_m24 ADNI_base2 2 76 y AD F x x x x m24

The base is constructed using all four time points. The time variable is given in years. I am using long_stats_slopes for aseg.stats as follows:

long_stats_slopes --qdec ./qdec/long_AD_NL_TP1_2_3_4.qdec.table.dat --stats aseg.stats --meas volume --sd $SUBJECTS_DIR --do-avg --do-rate --do-pc1fit --do-pc1 --do-spc --do-stack --generic-time --time years --stack-avg ./qdec/long_AD_NL_TP1_2_3_4

(similarly for ?h.aparc.stats)

Having in mind that TP1 and TP2, as well as TP2 and TP3 are separated approximately 6 months and TP3 and TP4 are separated approximately 12 months, are the annualized percent change or atrophy rates using this scenario reasonable (statistically?). Is it maybe more reasonable to apply the same scenario using three time points (for example TP1, TP3 and TP4 from the previous example and the template based only on these time points with the same approximate difference between all of them of 12 months, or TP1, TP2 and TP3 from the previous example and the template based only on these time points with the same approximate difference between all of them of 6 months)?

Best Regards,

Katarina Trojacanec, M.Sc.
Teaching and research assistant

Faculty of Computer Science and Engineering
Ss. Cyril and Methodius University - Skopje, Republic of Macedonia