[DDI-SRG] iIn-line data / defined range of values / data display format

[Joachim Wackerow]

Some additional thoughts on defined ranges/virtual recode below.

Wendy Thomas wrote:
> On Wed, 15 Aug 2007, Joachim Wackerow wrote:
> 
>> In the discussion with Larry Hoyle about a SAS converter I noticed
>> several things. Now I have three questions:
>>
>>
...

>> Defined range of values, CodeScheme / CategoryScheme
>>
>> Variables with interval or ratio measurement can have ranges of data
>> with different code values but same category labels.
>>
>> Example:
>> BMI
>>     low-<18.5 =  "Underweight"
>>     18.5-24.9 =  "Normal weight"
>>     25-29.9 =  "Overweight"
>>     30-high =  "Obesity"
>>
>> For such a variable it would make sense to define ranges of values
>> associated with the same category. A derived variable with a related
>> recode would be not necessary.
>>
>> For my understanding we have no possibility to represent this approach.
>>
>> A solution would be in Code of CodeScheme to have Range as a choice for
>> Value.
> 
> I am uncomfortable using "ranges" as a code scheme. This is, in effect, 
> an unrealized recode, simply providing the definitions of these terms in 
> relation to the ranges. In analysing the data it is designed to use, in 
> this case, the actual BMI. If I were using it as a category "obese" etc 
> I would recode this information either on the fly or by creating a new 
> variable (or overwriting the BMI variable). I would make a separate 
> scheme of virtual recodes and create a variable without a physical 
> representation.

As I said in the other email I agree on the unrealized recode. 
Additionally I have following thoughts:

A virtual recode realized by a defined range in the code scheme seems to 
be a comfortable approach for variables with grouped numbers or codes. 
It is not necessary to define codes for the groups nor to define a 
derivation command in the variable container. The information defined by 
Range would be enough for an application. What could be the disadvantage 
of allowing Range in CodeScheme/Code as a choice to Value?

A indicator for virtual variables would be in general helpful. So it is 
clear that this variable does not exist in the data set, only as a 
virtual derivation. When the virtual state is explicitly indicated, the 
variable can't be misunderstood as a variable just without a reference 
to a physical representation.

Achim