[DDI-SRG] [Fwd: Coded missing values]

[Wendy Thomas]

Missing values are often defined as missing for specified reasons "don't 
know", 'refused to answer", "did not respond" etc. In this case they are 
listed as categories and can be included in a code scheme as they have 
specified values. This is done in the logical product.

Is there not an implication that anything outside of a valid range or 
valid defined codes is invalid and therefore "missing"?

Prior to discussing this, can we come up with a list of use cases for 
expressing missing values both in the logical content and in various 
physical respresentations?

WEndy

I agree that we need a means of clearly expressing a "blank"

On Thu, 30 Aug 2007, Joachim Wackerow wrote:

> Pascal and others,
>
> It is possible to define a category without label, just stating the fact
> that the category is missing.
>
> A missing value seems to be an attribute of a category not of a code.
> The term 'value' of missing value is here a bit misleading, it is not
> the 'Value' of 'Code'. A code is just a code. A category gives the code
> a meaning.
>
> 1.
> A range of missing values seems to be convenient, but for my knowledge
> this kind of definition is only possible in SPSS. Nevertheless it is
> worth to think about.
>
>
> Here are additional thoughts on missing values.
>
> 2.
> I was wondering if it makes sense to define a missing value for a whole
> set of variables of for a whole study, which is common practice. I'm not
> sure if 'PhysicalDataProduct/MissingData' covers this sufficient.
>
> 3.
> Common practice is also to define a blank as missing value for numeric
> variables. I.E. SPSS would assign a system missing value. Currently it
> is possible to define blank as a string code in Code/Value like:
> '<Value> </Value>'. This seems to be error prone. A better approach
> would be to have an explicit definition for special codes like a blank.
> For example:
> <Value blank="true"/>
>
> 4.
> System missing values are not describable yet. But this seems to be
> important if a study is only available in SPSS or SAS. These values are
> represented as numeric values beyond the allowed real numbers internally
> in the statistical packages. Currently it would be only possible to
> recode the system missing value code to a valid numeric code described
> as missing category. This doesn't seem to be a good approach.
>
> In SPSS one system missing value code is available, in SAS several are
> available. Again an explicit definition of this system missing value
> codes would be desirable. The name of the system missing value is
> important and in addition the related scheme like SAS. For example:
> <Value missingValue="N" missingScheme="SAS"</>
>
> I have the impression that we should discuss the subject "missing
> values" on a conference call (topic 1-4, perhaps other ideas). The
> existing possibility to define a missing value seems to be not sufficient.
>
> Achim
>
> Pascal Heus wrote:
>> Further to the message below. in SPSS, I can also define a range of
>> coded missing values (like 10-20), is this something we'll support in 3.0?
>> thanks
>> *P
>>
>> -------- Original Message --------
>> Subject: 	Coded missing values
>> Date: 	Wed, 29 Aug 2007 11:47:23 -0400
>> From: 	Pascal Heus <pascal.heus at gmail.com>
>> To: 	DDI Structural Reform Working Group. <ddi-srg at icpsr.umich.edu>
>>
>>
>>
>> All:
>> I have a couple of questions on coded missing values (like -1=missing,
>> not system missing) :
>> - In DDI 2.0, missing values are flagged in the catgry element of the
>> variable. However, in SPSS, I can define missing value codes without
>> defining categories. In such case, is there a way to capture this in DDI
>> 2.0?
>> - How do we capture missing value codes in DDI 3.0? According to Wendy's
>> mapping, it goes into the l:category element. As in the SPSS example
>> above, I could however define a discrete code value that is not
>> associated with a l:category but represent a missing value. Should I
>> file this issue in Mantis?
>> thanks
>> *P
>>
>> --
>> Imagination is more important than knowledge.
>> - Albert Einstein
>> www.quotator.net
>>
>>
>>
>> --
>> Do not dwell in the past, do not dream of the future, concentrate the mind on the present moment.
>> -- Buddha
>> www.quotator.net
>>
>>
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Wendy L. Thomas                          Phone: +1 612.624.4389
Data Access Core Director		 Fax:   +1 612.626.8375
Minnesota Population Center              Email: wlt at pop.umn.edu
University of Minnesota
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