[DDI-users] standard missing values via DDI

[Adrian Dușa]

Dear All,

Following a private discussion, an idea emerged that i think it's useful to
circulate and discuss.

>From what I understand, SAS codes special missing values as extremely low
values, while Stata went for the opposite way, coding them as extremely
large values.

Those are decisions which are software specific, and it is unlikely that
other software packages will follow one trend or another.

There might be a way to solve all particular needs, using DDI as a mediator
and most importantly using only "normal" values.

The main quest is to differentiate between missing values. In R, and I'm
sure DDI can do that too, each variable can be attached with a list of
attributes. One such component of the list of attributes could be dedicated
to the missing values, and further differentiate within:
- "missing at random": 1, 5, 9
- "missing by design": 8, 15, 78

Here, the (simple integer) numbers 1, 5, 8, 9, 15 and 78 are nothing but
the indexes of the line numbers (ie the cases) where the missing values
reside in a particular variable.

If I had this kind of information in the DDI XML file, I could then
instruct my R function to create <specific> setup files for SAS or Stata
using .r and .d in those specific cases, while in R all missing values
could remain as simple NAs but users can still differentiate between
missings by just looking at the list of attributes.

This way it would accomplish the other need to avoid accidental mistakes,
and it is both package independent and specific in the same time, using DDI
as an exchange platform.

Recoding specific missing values is trivial in R, but I have to confess I
don't know if and how this might be done in other software via setup files.
People using specific software packages might confirm if this approach is
possible or not. Raw data should be read by all packages from a .csv file
where missing values are system missing (empty) values.

Best wishes,
Adrian


-- 
Adrian Dusa
University of Bucharest
Romanian Social Data Archive
1, Schitu Magureanu Bd.
050025 Bucharest sector 5
Romania
Tel.:+40 21 3126618 \
        +40 21 3120210 / int.101
Fax: +40 21 3158391
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