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Missing Value ReasonSmall Group Report to the VCDE WS F2F

June 17, 2005• Harold Solbrig

• David Aronow

• Rebecca Crowley

• Jim Kadin

• Kim Klingler

• wiki

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Formerly known as Flavors of Null,

FoN became Missing Value Reasons

Changed name as clarified focus of Group– “Null “ is ambiguous (reserve for status of a cell in

a database, when nothing is posted to that cell)– Realized we are concerned with situations in which

a ‘meaningful’ data value is not available– CDE development efforts often desire to support

explanation of why ‘meaningful’ values are not available

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This Report….

• We have achieved some conclusions, which will be presented in this Report

• But fundamental questions remain unresolved – issues we will also raise in this report, for your consideration

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“Meaningful” values v. Missing values

• A working definition of ‘meaningful’ might be that a ‘meaningful’ value ‘answers’ the ‘question’ posed by a data element

• In contrast, a Missing Value Reason ‘answers’ the implicit ‘question’ “Why is there no ‘meaningful’ value, when there is none?”

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MVR Scope• MVR can apply to all data types –

enumerated, date, number, string, etc.• For non-enumerated CDE, the MVR are

recorded in a data field separate from the ‘meaningful’ value

• For enumerated CDE, the MVR can be recorded in either the same data field as, or a separate data field from, the ‘meaningful’ value (details later)

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Vocabulary v. Applications

Missing Value Reasons are defined and used in terms of vocabulary and CDE (the currency of exchange between information systems), not in terms of application or database design or implementation.

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MVR may not only be MVR• Terms may be MVR in one application context,

but not in another context• Example: Not specified

– In an automated data feed of lab result nominal values such as ‘High’, ‘Low’, etc., the value ‘Not specified’ explains why a ‘meaningful’ value was missing

– For CDE Self Reported Person Sex Text Type, the value ‘Not specified’ means, in part, undifferentiated, which is a ‘meaningful’ answer

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MVR and EVS• EVS should be robustly stocked with terms that cover a

broad range of MVR which can be extended as needed • CDE curators can select terms from the EVS stock as

needed• We recommend harvesting a EVS starter set of MVR

from the HL7 NullFlavor and the CDC Draft Missing Values lists, and expanding the set based on caBIG CDE and use cases

• HL7 arranges NullFlavor values hierarchically, which the MVR Small Group has discussed, but for which the Group has not yet arrived at a recommendation

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Recommendation to Application Developers

For each specific application/message context, is documentation of a MVR a requirement?

• If required, build the application to force MVR documentation

• If optional, build the application to accept MVR documentation, but not require it

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Recommendations to CDE Curators:MVR Implementation Methods

• There are two methods for implementing MVR:1. Include MVR values as permissible values for an

individual enumerated CDE

2. Create an associated MVR-CDE that enumerates MVR permissible values for an individual CDE

• Examples follow….

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1 – MVR as CDE permissible values• Gender – Permissible values

• Male• Female• Unknown• Not Specified

• Lab Test Summary Result – Permissible values• Normal• Abnormal High• Abnormal Low• Pending• Not available from lab system

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2 – MVR as their own MVR CDEto be used when a ‘meaningful’ value is missing

and a MVR needs to be identified and linked

• Gender CDE – Permissible values• Male• Female

• Gender MVR CDE – Permissible values• Unknown• Not Specified

• We are also considering a role for category MVR CDE, such as for physical exam findings or lab tests

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Other CDE Curator Recommendations• Explicitness in value names is desirable

– “Uncertain disease progression” is more explicit than “Uncertain”

– “Uncertain” could mean that the data entry person was uncertain if disease progression was evaluated, an MVR

– Explicitness allows differentiation of a ‘meaningful’ value from an MVR

• Value meanings should be used to clarify the intent or role of MVRs

• When MVRs are included in CDE permissible value display lists, separate the ‘meaningful’ values from the MVR

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Differences in Perspective• The MVR small group is not of one mind regarding

the relative value of the two MVR implementation methods

• These differences represent different views– regarding the degree to which the VCDE, and indeed

caBIG as a whole, should be prescriptive v. descriptive in its standards

– regarding the role of architecture in the support of MVR functionality

• We have also not concluded our discussion of Recommendations to Application Developers

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Next Steps

1. VCDE feedback on the recommendations so far and the strategic open issues

2. MVR Small Group continues to clarify and describe the open issues

3. MVR Small Group engages the VCDE and Architecture WS on resolving the open issues

4. Wiki with us…..

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Wikihttp://informatics.mayo.edu/wiki/index.php/CaBIG_Flavors_of_Null

Username = wikiPassword = wikiwiki

• Discussion, meeting minutes, decisions, use cases, links• Editable off line and during meetings• Need for housekeeping and concern with editing other

author’s material• Takes a little practice, but it doesn’t break