Re: [R] Missing data and LME models and diagnostic plots

2009-10-21 Thread Mark Difford
Hi Peter, >> See e.g. Hedeker and Gibbons, Longitudinal Data Analysis, which >> repeatedly stresses that >> mixed models provide good estimates if the data are missing at random. This may be true. However, one of the real strengths of LME is that it handles unbalanced designs, which is a differ

Re: [R] Missing data and LME models and diagnostic plots

2009-10-21 Thread Kingsford Jones
Mixed models based on likelihood methods can often handle missing observations within subjects, but they not do well with missing individual elements in the design matrices (think unit nonresponse vs item nonresponse in the survey world). Continuing with the example I recently sent to you set.see

Re: [R] Missing data and LME models and diagnostic plots

2009-10-21 Thread Peter Flom
I wrote >>> I am puzzled by the performance of LME in situations where there are >>> missing data. As I >>> understand it, one of the strengths of this sort of model is how well it >>> deals with missing >>> data, yet lme requires nonmissing data. > Mark Difford replied >You are confusing mi

Re: [R] Missing data and LME models and diagnostic plots

2009-10-21 Thread Mark Difford
Peter Flom wrote: >> I am puzzled by the performance of LME in situations where there are >> missing data. As I >> understand it, one of the strengths of this sort of model is how well it >> deals with missing >> data, yet lme requires nonmissing data. You are confusing missing data with an

[R] Missing data and LME models and diagnostic plots

2009-10-21 Thread Peter Flom
Hello Running R2.9.2 on Windows XP I am puzzled by the performance of LME in situations where there are missing data. As I understand it, one of the strengths of this sort of model is how well it deals with missing data, yet lme requires nonmissing data. Thus, m1.mod1 <- lme(fixed = math_