Friday, June 16, 2017

SDTM, XPT and the constitution

Imagine that the constitution of your country would state "cars must be powered by gasoline".
Would you find that acceptable?
Now, we all know that most cars are powered by gasoline, but such a statement in the constitution would give electrical cars no chance at all, even when these are more friendly to the environment.

Something very similar happens at CDISC: the new SDTM Model v.1.6 (so not the Implementation Guide) has been written with only 1 implementation in mind: SAS-XPT format.

Standards models should be developed and published independent of the transport format. A very good example is HL7-FHIR for which there are three technical implementations: XML, JSON and RDF. The documentation has been published in a transport format independent way. It is only when you go to the examples (which you can consider as an Implementation Guide) that you will see something about the transport format.

So, as part of the public review of the SDTM Model v.1.6, I asked the SDTM team to change the text of the model in such a way that it is transport format neutral. This would then allow other transport formats such as XML (e.g. Dataset-XML), JSON and RDF for porting SDTM data in the future.

My request was turned down.
Here is the justification of the SDTM team (snapshot from the JIRA site):

"Considered for future" is the usual expression of the team for "refused".

This answer is indeed a "doom loop": it gives the FDA a reason for further refusing to allow a modern format. When asked about it, they can then say "we can't do that, it is not allowed by the SDTM model".

I have been observing in the last 5-10 years that the SDTM model and standard has been evolved in such a way that all first principles have been thrown away, such as avoidance of data redundancy, no derived data, and separation between model and implementation. This makes it more and more difficult to implement and ruins data quality. Essentially, one can say that it has been steered into a "dead end".

How can this be changed?
I must honestly say that I do not know the answer. "The train has left the station, but is it on the right track?" is a question that is even not posed within CDISC, and especially not within the SDTM team. Maybe the team needs some strong guidance itself, or responsibilities must be reassigned. There are some bright progressive people within CDISC but these are not involved in SDTM. Maybe it is time to give them the lead in SDTM development.

1 comment:

  1. I agree, Jozef. One of the unfortunate consequences of this stubborn resistance is that it effectively cuts off SDTM from being considered as a valid model for other research and analytical purposes other than submission to FDA and PMDA, since other technical experts might dismiss it as hopelessly obsolete. It's way past time to make the model more generalized, and let the SDTMIG for XPT deal with the limitations and restrictions of XPT. Perhaps this would inspire others to try to use the SDTM for other use cases, extending its reach and future lifespan.