In my earlier posting on SDTM as a Cookbook, I described an alternative approach for defining new domain models for use with CFAST Therapeutic Area User Guides (TAUGs). Based on an internal poll of SDS team members, there seems to be a desire to create many domain models (a predilection toward splitting, rather than the lumping approach I favor). Yet creating new domains is a frustrating and lengthy process. Although these are now mostly being modeled by CFAST teams with very specific use cases, there has been a tendency to also vet them through SDS in a more generalized form as part of a batch associated with a future SDTMIG release, a process which can take 2-3 years or more. In the meantime, TAUGs are faced with proposing draft domain models under a stricter timeline, well before they exist in the officially sanctioned normative SDTMIG world.
What a waste — and it gets worse. Once the domain is issued as final as part of an SDTMIG version update (indeed, that’s assuming the SDS team consensus allows it to and it actually passes the comment process) it now has to be evaluated by FDA before they can determine whether they’re ready to accept it. Although 15 TAUGs have been posted to date, the FDA has yet to clearly indicate their readiness to accept any of them. And the acceptance process has also been excruciatingly long (it took nearly 2 years for FDA to announce readiness to accept SDTMIG v3.2 – even then with some restrictions). In the meantime, people simply make up some other approach to get their daily work done – the antithesis of standards.
Let’s take a current example of how we may have applied the cookbook approach to draft domains included with the just-posted TAUG-TBv2. This TAUG includes 5 new draft domains as well as revisions to 3 existing domains which are presented as SDTMIG domain models. One of the new domains (which was vetted with SDTMIG v3.3 Batch 2 and also used in Asthma but not yet released as final) is the RE (Respiratory Physiology) domain. This is a Findings General Class domain, which is mostly consistent with the current version of the SDTM v1.4 except for the addition of 3 new variables: REORREF, RESTREFN and REIRESFL. (An earlier version of this domain was also included in the Asthma and Influenza TAUGs.)
Now a cookbook recipe might present this RE domain as a list of steps to follow to “roll your own” domain. Instructions might include:
- Create a new custom domain with the standard identifiers and all variables from the SDTM v1.4 Findings General Class.
- Assign the Domain Code and prefix “RE” from controlled terminology.
- Insert the standard timing variables that are typically provided with a Findings Physiology domain.
- Create the following 3 new Non Standard Variables (NSVs):
(Note definitions for these might be pulled from a newer version of the SDTM which is now being updated more frequently, or else from a CDISC Wiki resource).
- Remove any unnecessary or irrelevant permissible variables such as REMODIFY, RETSTDTL, etc. – just like you do with published domains. (Note that these are all permissible variables – assigning a new NSV as Required or Expected would be a complication, but this would be an odd choice for a newly created variable anyway).
- Add any additional NSVs in the usual manner (this would be much smoother if the new proposed method of putting NSVs in the parent domain was adopted).
- Apply other controlled terminology bindings for variables within the domain (such as RECAT, RETESTCD, etc. that are declared in a sample define.xml file that’s posted along with the recipe.
As the output of this exercise one would normally create the define.xml metadata for the domain as well as a RE.XPT file (which will later be populated with data values). The sample define file included with the recipe would also specify which controlled terminologies apply to both the standard and new non-standard variables (I assume that new terminology values that would be intended for use in this domain would be created through the normal terminology request process, and simply referenced in the define-xml example). The recipe could still provide a draft domain in the usual Word Table or Excel format – but this would be presented as an example rather than a normative specification, similar to including an illustration or photo in a recipe.
I believe it should be sufficient to apply the standard class-level validation rules (which include checking for controlled terminology assignments), which can be addressed separately from the domain model, so there should not be any specific new user acceptance testing required by FDA. FDA might also specify separate content-based checks they may want, but these can be added at any time later, once they’ve had a chance to review submissions using this model. But new rules can also be added outside the IG. And while it will be technically a non-binding custom v3.2 domain in each submission, if it’s conforming to the recipe (which can be clearly stated in the define) it can serve the same purpose as a new SDTMIG domain in a future version. The difference is that it can be put directly into use. A beneficial side effect is that this also encourages early testing among the research community, which might result in beneficial tweaks to the recipe, which can be maintained over time and augmented with more and more examples suggested by adopters in a crowd-sourced Wiki sharing environment, which should only serve to make the domain model more solid over time. Sure, this might require review and curation by the SDS team, but that should be a lot less onerous than the current process.
The benefits of such an approach include:
- Making it simpler and easier to create new domain models based on existing published versions, which might help shorten the development time for TAUGs
- Allowing sponsors to adopt these new models more rapidly without waiting for new domains or FDA announcements
- Making it possible for FDA to accept these models without a lengthy acceptance process
- Providing an improved, rapidly evolving Wiki-based knowledge resource to help sponsors address representation of data that doesn’t fit in existing final domains in a more consistent manner.
- Minimizing the number of new versions of the SDTMIG that have to be handled by industry and regulatory authorities.
Of course, adopting such an approach is not trivial. It would require buy-in by FDA and industry, and would require new methods for sharing these recipe guidelines (probably via the Wiki) and a whole lot of communication and training. But it seems to me it would be a much more practical way to move forward to extend the reach of the SDTM for new TAs in a leaner, quicker manner with fewer maintenance and version management headaches.