I like the missing at random conditionally term - MARC For informative missing or non-ignorable non-response let's also come up with a better term. I seldom see anything that is ignorable in statistics. One "straw man" would be missing at random conditionally on unknowns or MARCU; a better one might be missing dependent on unknown response or MDUR. I'm sure others can improve on this. It's fun coming up with new names; getting them used is another matter.
-Frank Harrell Werner Wothke wrote: > > Rod: > > Sorry, I have to side with Seppo Laaksonen on this one. I teach missing > data handling to applied social scientists as part of my structural > equation modeling workshops. In my experience, the MAR-MCAR distinction > is confusing at best. For non-statisticians, these two terms simply > *sound* too similar to make a meaningful distinction. In addition, > people's common-sense understanding of the term "missing at random" > is really MCAR. This is reflected in Seppo's desire to change the > "MAR" terminology to "missing at random conditionally." In other words, > the MAR-MCAR terminology is somewhat of an obstacle to teaching > ML-based missing data methods to non-statisticians. > > I do not mean to diminuish Don Rubin's eminent contributions to the > missing data field in any way--quite the contrary. On the other hand, > after 27 years of MAR-MCAR it is really time to consider replacing that > terminology with one more easily understood by applied researchers. > Yours and Don's assistance in this matter would help a lot. > > Cheers, > > Werner Wothke, Ph.D. > > Rod Little wrote: > > > > Dear Seppo: you are not the first to make such a comment. I'd say that MAR > > is one of the few terms in the area I like, since it at least has a > > well-defined meaning! It was originally coined in Rubin's 1976 Biometrika > > paper, and the rationale was that people were doing analyses ignoring the > > missing data mechanism that had an implied assumption, and he defined MAR > > to be that implied assumption. For likelihood inference that assumption is > > MAR. Since there is another reasonable term for the "randomness" you are > > talking about, namely missing completely at random, I see no real problem. > > There is an strong argument that people who write the seminal article > > should get to define terms, and I think trying to change a definition is > > asking for confusion. > > > > Concerning other terms, is there an established definition of > > "informatively missing"? I'd be interested in comments on this. Best, Rod > > > > On 29 Mar 2001, Laaksonen Seppo wrote: > > > > > I do not like about the term MAR, missing at random. Of course, when it > > > has > > > been defined, there are no problems. But the direct interpretation of > > > that term > > > is confusing, since missingness is not random in this case but > > > conditionally in > > > some sense. The term should be something like missing at random > > > conditionally > > > (MARC) or MAR according to covariates. I am not fully satisfied to those > > > terms. > > > What do you prefer? > > > > > > Best regards > > > Seppo Laaksonen > > -- > *********************************************************************** > * * > * SmallWaters Corporation phone: USA-773-667-8635 * > * 1507 E. 53rd Street, #452 fax: USA-773-955-6252 * > * Chicago, IL 60615 e-mail: [email protected] * > * USA web page: http://www.smallwaters.com * > * * > *********************************************************************** -- Frank E Harrell Jr Prof. of Biostatistics & Statistics Div. of Biostatistics & Epidem. Dept. of Health Evaluation Sciences U. Virginia School of Medicine http://hesweb1.med.virginia.edu/biostat
