topic NOMCAR Option: How Does SAS Perform Taylor Series Variance Estimation with Missing Values? in SAS User Groups Discussions

NOMCAR Option: How Does SAS Perform Taylor Series Variance Estimation with Missing Values?

peggy3223 — Wed, 03 Jun 2026 03:47:41 GMT

Dear SAS Community,
I am currently using PROC SURVEY procedures (such as SURVEYMEANS, SURVEYLOGISTIC) to analyze complex survey data and have some questions regarding how the NOMCAR option handles missing values in variance estimation.

According to the SAS documentation and related papers, when the NOMCAR option is specified, SAS treats observations with and without missing values for the analysis variable as two different domains. It then calculates the point estimates (e.g., mean, sum) only in the non-missing domain and performs a domain analysis for Taylor Series variance estimation.

My questions are:

1. During the Taylor Series linearization and variance estimation process, how exactly does SAS handle the observations that have missing values?
2. Although these missing observations do not contribute to the point estimates, how do they contribute to the final variance estimation (for example, their impact on strata, clusters, and weights)?
3. Are there any more detailed mathematical explanations or algorithmic descriptions available that can help me understand how NOMCAR works internally within the Taylor Series framework?

I have already reviewed the following materials but could not find more technical details on the exact computation:

SAS Official Documentation: The SURVEYMEANS Procedure (section on NOMCAR and Missing Values)
SAS Official Documentation: The SURVEYLOGISTIC Procedure (section on NOMCAR and Missing Values)
Gorrell, P. (2009). Survey Analysis: Options for Missing Data. NESUG 2009 Proceedings.

If anyone has come across more in-depth technical documents, SAS Help Center, or example code that illustrates this process, I would greatly appreciate your guidance.
Thank you in advance for your help!

Re: NOMCAR Option: How Does SAS Perform Taylor Series Variance Estimation with Missing Values?

sbxkoenk — Wed, 03 Jun 2026 15:34:42 GMT

That's a fair question... but I don't know the answer either.

Maybe you can try some Google searches:

NOMCAR SURVEY Taylor variance estimation SAS site:lexjansen.com
NOMCAR SURVEY Taylor variance estimation SAS site:communities.sas.com
NOMCAR SURVEY Taylor variance estimation SAS site:blogs.sas.com
NOMCAR SURVEY Taylor variance estimation SAS site:support.sas.com
NOMCAR SURVEY Taylor variance estimation SAS site:documentation.sas.com

And finally, you can ask an LLM
NOMCAR SURVEY Taylor variance estimation SAS How do missing values contribute to the final variance estimation?
, but be aware ...

AI responses may include mistakes.
So, double-check important info!
For AI-generated content, please evaluate accuracy and suitability before use.

BR, Koen

Re: NOMCAR Option: How Does SAS Perform Taylor Series Variance Estimation with Missing Values?

sbxkoenk — Wed, 03 Jun 2026 14:46:20 GMT

Maybe @SAS_Rob and / or @jiltao can help you out.
You can also contact Technical Support directly.

SAS Technical Support:
Here is a link for your convenience: https://support.sas.com/en/technical-support.html#contact

BR, Koen

Re: NOMCAR Option: How Does SAS Perform Taylor Series Variance Estimation with Missing Values?

peggy3223 — Thu, 04 Jun 2026 09:56:02 GMT

Thank you for your response！

Re: NOMCAR Option: How Does SAS Perform Taylor Series Variance Estimation with Missing Values?

SAS_Rob — Thu, 04 Jun 2026 14:06:05 GMT

Using the NOMCAR option essentially treats the observed and missing observations as two separate domains. What this does practically is to include an indicator function in the weights function.

See this section of the documentation.

SAS Help Center: Domain Analysis

The Vhij that is defined there would then be plugged into the Taylor Series formula wherever you see Whij:

SAS Help Center: Variance Estimation