Re: [NMusers] NONMEM vs. R for linear mixed-effects
I omitted one critical piece of information:
I think that your approach implies an order to the data from different =
periods — whereas making PERIOD=ID allows NONMEM to see each =
treatment as a separate subject (i.e., the random effect)
Dennis Fisher MD
P < (The "P Less Than" Company)
Phone / Fax: 1-866-PLessThan (1-866-753-7784)
> On Feb 28, 2018, at 9:23 AM, Leonid Gibiansky =
> Just checking: you have treatment effect in R but no effect in Nonmem, =
am I correct? (I have not used R nlme for a long time, may be I am =
interpreting it incorrectly)
> Should you code nonmem as
> INTERCEPT = THETA(1) + THETA(3)*PERIOD + ETA(1)
> SLOPE = THETA(2) + THETA(4)*PERIOD + ETA(2)
> Y = INTERCEPT + SLOPE * TIME + EPS(1)
> On 2/28/2018 11:16 AM, Dennis Fisher wrote:
>> I am implementing a linear mixed-effects model in R.
>> Out of curiosity (and to confirm that I was doing the right thing), I =
wrote the code initially in NONMEM, then tried to replicate the results =
>> The dataset is four (identical) treatments for one subject and the =
data are reasonably linear.
>> For most subjects, the results from the NONMEM analysis are nearly =
identical to those from R.
>> But, for one subject, the SLOPE/INTERCEPT are sufficiently different =
to concern me that I am implementing one of these (or possibly both) =
>> The critical code is:
>> $PREDINTERCEPT= THETA(1) + ETA(1)
>> SLOPE= THETA(2) + ETA(2)
>> Y= INTERCEPT + SLOPE * TIME + EPS(1)
>> *R: LMER package:*
>> lmer(DV ~ TIME + (1|PERIOD), data=DATA, REML=FALSE)
>> DV is the dependent variable
>> PERIOD distinguishes the treatments (and is a factor)
>> *R: NLME package:*
>> lme(DV ~ TIME, random = ~ 1|PERIOD, data=DATA, method="ML")
>> The two R packages yield identical results.
>> Graphics from NONMEM and R differ slightly but there is no obvious =
preference between these approaches.
>> Any thoughts as to a possible explanation?
>> Dennis Fisher MD
>> P < (The "P Less Than" Company)
>> Phone / Fax: 1-866-PLessThan (1-866-753-7784)
>> www.PLessThan.com <http://www.plessthan.com/> =
Received on Wed Feb 28 2018 - 12:27:00 EST
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