Re: How to monitor the variation in time ?

Well I dont know how much it help but you are talking about correlated
linear model.

Let say

Y = A concentration value
Then for testing time effect you can fit

Y = alpha + Beta*Time + Err

where Err is distributed as Normal(0,V). Where V is variance
covariance matrix.

V is not sigma_Square Identity. The structure of V depends on your
problem.

But you can fit this model using SAS Proc GLM or MIXED routine.

.

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