last 3 time points [🇷 for BE/BA]

posted by martin  – Austria, 2008-10-12 02:04 (6092 d 23:06 ago) – Posting: # 2519
Views: 22,053

dear Yung-jin Lee !

good to hear that your code will be much more sophisticated than WinNonLin! I appreciate your efforts. you may find of interest that in the case of manual selection of the last 3 time points, the middle time point is “useless” to calculate lambda_z by using the OLS fitting criteria in the case of equidistant measurement time points. in this case, the middle data tuple only effects the intercept but not the slope (=lambda_z). you may think about implementing a warning message in this case.

the theoretical background for this unexpected behavior rather complicated but I can provide you some information upon request.

some examples:
t <- c(10, 12, 14) # equidistant time points
c1 <- c(5, 4, 1)
c2 <- rnorm(3)
c3 <- runif(3)

lm(c1~t)
lm(c1[-2]~t[-2])

lm(c2~t)
lm(c2[-2]~t[-2])

lm(c3~t)
lm(c3[-2]~t[-2])

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