Hi, Cliff Nanda and I just briefly discussed your question on the median value calculation. We come up with two options: 1. The median income should be available for each Census Tract. You can take total households for each census tract as weights, using the weighted average for the median household income across these Census Tracts. Then MOEs can be calculated using the formula of weighted mean. 2. You can combine the distribution of household incomes for each census tract and derive a single distribution for aggregated Census tracts. Then you can come up with a median value. Using these methods, you will need to interpolate MOEs for the upper bound and the lower bound. Both these methods will not give you the real median values - they are only ballpark figures. But you can definitely try both and see which one is better. Liang Long Cambridge Systematics, Inc. 4800 Hampden Lane Suite 800 Bethesda, MD 20814 tel 301 347 9141 fax 301 347 0101 FHWA 202-366-6971 e-mail llong(a)camsys.com www.camsys.com ctpp-news-request(a)chrispy.net Sent by: ctpp-news-bounces(a)chrispy.net 01/03/2011 02:39 PM Please respond to ctpp-news(a)chrispy.net To ctpp-news(a)chrispy.net cc Subject ctpp-news Digest, Vol 83, Issue 1 Send ctpp-news mailing list submissions to ctpp-news(a)chrispy.net To subscribe or unsubscribe via the World Wide Web, visit http://www.chrispy.net/mailman/listinfo/ctpp-news or, via email, send a message with subject or body 'help' to ctpp-news-request(a)chrispy.net You can reach the person managing the list at ctpp-news-owner(a)chrispy.net When replying, please edit your Subject line so it is more specific than "Re: Contents of ctpp-news digest..." Today's Topics: 1. How to Combine Median Values for Mutliple Areas (Cook, Cliff) 2. RE: How to Combine Median Values for Mutliple Areas (Eric Kramer) ---------------------------------------------------------------------- Message: 1 Date: Mon, 3 Jan 2011 13:24:06 -0500 From: "Cook, Cliff" &lt;ccook(a)cambridgema.gov&gt; Subject: [CTPP] How to Combine Median Values for Mutliple Areas To: &quot;ctpp-news(a)chrispy.net&quot; &lt;ctpp-news(a)chrispy.net&gt; Message-ID: &lt;600EBD94B0166D4BADC1083702EC47C4026F6C522B(a)Mordac.City&gt; Content-Type: text/plain; charset="us-ascii" I am looking for guidance on how to combine median income values for several census tracts into a single value and associated margin of error. I recall seeing something about this topic in an ACS document but cannot locate the information at this time. Any help would be appreciated. Cliff Cook ----------------------------------------------------------------------------- Clifford Cook Planning Information Manager Cambridge Community Development Dept. 344 Broadway Cambridge, MA. 02139 617/349-4656 FAX 617/349-4669 TTY 617/349-4621 email => ccook(a)cambridgema.gov web site => <http://www.cambridgema.gov/~CDD/>