Ten More Things to Know (and Do) About the American Community Survey

Keys to Understanding and Accessing the Data
John Blodgett, Missouri Census Data Center
1. Manuals   |  2. Geography   |  3. Data Profiles, MCDC   |  4. Data Profiles, Census   |   5. Trend Data   |   6 - 10


(Note: If your browser supports zooming we suggest you view these pages zoomed to 120%)

A few years ago (2007) we created ">Ten Things to Know about the American Community Survey", which became one of our most popular, most frequently visited and linked-to pages. Its purpose was to provide a general overview for people just getting started with this relatively new and important data resource. That page is a little bit dated now (Item 2 is about the limitations of the 2005 data release, which is not really much of an issue any more), but most of what was true and important then is still true and important today.

But some things have changed, a few pretty dramatically, in the three years since "Ten Things ..." was written. The ACS has gotten a bit more complicated. We now have things called Three Year Period Estimates and we are less than a year away from the first of the long awaited Five Year Period Estimates, which we have been promised will give us all our favorite small-area geography back.

One of the things that has happened regarding the ACS is that a lot more people have started using it. It is not quite the mystery resource it was back then. The Census Bureau has enhanced the way the data can be accessed via their American FactFinder web query tool, and they have also been creating all kinds of metadata and tutorial material to help users. Several of the things we'll be talking about here will involve these new materials.

We here at the Missouri Census Data Center have been busy as well, creating a number of resources to assist users in finding and accessing the American Community Survey data. We have created our own set of data profiles (modeled after but significantly different from those available from the Census Bureau) and, for us data junkies, datasets that can be accessed using our Uexplore/Dexter software tools. Several more of the items ("things") being covered here will reference these resources.

You'll notice right away that this document is considerably longer than its predecessor. It is actually a suite of three documents (web pages). Things 1 to 5 are covered on this ("Page 1") document, which then links to Page 2 where the remaining five items reside. Except that one of the items dealing with accessing the data in our data archive winds up getting a separate web page all to itself. You should also notice that we have a lot more graphics (mostly screen shots) in this document.

Note on how best to view this page. This document and its companions (page2 and item8) can best be viewed with a browser Zoom setting of about 120% (requiring that you have a fairly recent browser, since the Zoom option is a relatively new feature for the IE and Firefox browsers). To get this zoom level on most modern browsers you can hold down the CTRL key and hit the + key twice. (Use CTRL-0 to return to the normal 100% zoom setting.) Increasing the zoom level will make the embedded images much easier to read and the text should still fit across your screen once you center it.

  1. Read the Friendly Manual(s). (All but the most casual user). The Census Bureau has created an extensive set of reference products for the ACS which they refer to as the ACS Compass Products. If you go to the American Community Survey Home Page at the Bureau's web site and select the "How to Use the Data" tab from the orange bar of tabbed topics across the top, it takes you to the very helpful "How to Use the Data" page, which in turn features a description of and link to the ACS Compass Products page. There are actually three types of Compass products (e-training modules (coming soon) & powerpoint packages, in addition to the handbooks) but the one we want to highlight here is the series of Compass Handbooks. These provide user-friendly information about the ACS and the new multi-year estimates available in 2008. Each handbook targets a specific user group, including first time ACS data users. There are now (early 2010) a dozen of these handbooks available. These are not really a dozen independent publications; they all share the same basic information, but then have some specially targeted materials aimed at a certain class of user (such as "General Data Users", "Business Community" or "State and Local Governments"). These are pdf files that run about 65 pages, including about 40 pages taken up with a Glossary and 8 Appendices, which vary widely in general relevance and degree of difficulty. (High quality hard-copy versions are also available from the Bureau. A good way to get hold of one of these is to attend one of the MCDC's workshops.) You certainly do not have to read the entire booklet to get a good handle on what the ACS is all about. But it wouldn't hurt if you read (or at least skimmed) most of it at least once. You can always come back to the sections written by, if not exactly for, statisticians. The version I keep on my desktop is subtitled "What State and Local Governments Need to Know" and is 63 pages long (including a 3-page Glossary and 27 pages of Appendices) and a rather nice mostly purple cover. And if it were me and I was brand new to the ACS I would read our Ten Things to Know... page before starting on one of these manuals.

  2. Get a Handle on the Geography. (All users). Like most things coming from the Census Bureau, most ACS data products consist of data aggregated to various geographic areas: states, counties, cities, census tracts, school districts, etc. You really cannot use the products effectively unless you have a good basic understanding of the geographic dimension of the data. The Census Bureau provides an Overview of Geographic Areas page that is must-read material for anyone hoping to get data out of the ACS. The page currently (early 2010) deals with the units for which there are 1-year and 3-year estimates. At the end of 2010 (possibly the very beginning of 2011) there will begin to be 5-year estimates, at which time this page is going to get considerably larger as a whole new set of geographic entities (such as ZIP codes, state legislative districts, census tracts and even block groups) will be added. The first summary table ("1a") is a very informative document:

    If you understand what this table is telling you then you have a reasonable expectation of being able to make productive use of ACS data. Conversely, you really cannot afford to pretend that this information is not relevant to you (perhaps because half the area types you have no knowledge of nor interest in). It is not the specific Count values shown that are so important; it is the understanding of the role of population thresholds in determing which areas get which kind of data. For example, the 5th row of this table has statistics for the County geographic level. It shows you the Summary Level Code for counties (050) and indicates that of the total number of such areas (3,220) only 802, or 24.9%, have a population of 65,000 or more, while 1,887, or 58.6%, have populations of 20,000 or more. Why are these figures so relevant to the ACS? Because this means that less than a fourth of the counties in the country are large enough to have 1-year data published for them. Just under 60% are large enough to get data based on 3 consecutive survey years. This leaves a little over 40% of the nation's counties which will only get data based on 5 consecutive years of data (and which currently have no ACS data published for them).

  3. Access ACS Data as Profiles on MCDC Site. (All users.) We have a big jump here, as we go from pages you access to get a handle on the data, to ones that actually let you access the data. A "profile", in Census terminology, is a report that focuses on a single geographic area, and provides carefully chosen key indicator data to help you get a quick overview of that area. Profiles typically have a subject area or theme associated with them; so we have "economic" profiles, "demographic" profiles, "social" profiles, etc. We are going to point you to a pair of web sites for accessing similar (but not identical) ACS profile reports, one at the Census Bureau and one at the Missouri Census Data Center site. Though very similar in content, you'll notice significant differences in presentation format and linkages.

    If you are almost anywhere on the Missouri Census Data Center (MCDC) web site you should see a light blue navigation box (usually on the upper right hand side of the page) labeled Quick Links. The first link within this box is ACS Profiles. Following this link takes you to the main menu page for the MCDC ACS Profiles dynamic report generator. The front end here is fairly simple. You get to choose from 3 drop-down menus across the top: a time period (single year and 3-year choices are all we have at this point); a state; and an Area Type (i.e. a geographic unit). Based on your choices from these 3 drop-downs you will see the available choices in the dynamically-generated select list on the left of the screen. So, for example, if you choose the 2006-2008 time period (the default), Missouri as the state (again, it's the default), and Places (Cities) as the type of area, what you should see in the select menu is a list of all cities in Missouri that had 3-year data for this 3-year time period. That is basically cities of 20,000 or greater population. You can now choose any city or cities (up to 4) from the choices displayed. As you click on city names they are chosen; no need to hold down the ctrl key to get multiple choices. So you could, for example, click on Columbia city, Missouri and Jeferson City city, Missouri. The chosen areas appear in the "cart" window on the right. There is a buttom that allows you to clear this window and start over with your choices. Having chosen these two cities you still have the option of making more choices; the application allows up to 4 geographic areas to be chosen. You can return to the 3 menus across the top and change any of those that you wish (though if you change the Time Period it will clear your cart and you basically have to start over.) But you can easily go back and change the Area Type to State and choose Missouri as an area to be added to your cart. You could then also choose Nation as the Area Type and add a U.S. summary to your geographic choices cart window. The order in which you make your choices is singificant in that this is the left-to-right order in which the data will appear in the profiles. Here is what the menu page looks like after making these choices:

    Note that we also have some checkboxes across the bottom corresponding to the four sub-profiles (Demographic, Economic, Social and Housing) that can be used ("unchecked") to be selective about which of the four topics are of interest. At this point click on the Generate Report button and ... typically in about two or three seconds ... you should see something like this appear:
    Use this URL to bypass the menu and display this report as specified. Then you can scroll down and see the entire report, which is rather lengthy (it takes 12 pages when printed). There is actually quite a bit that can be said about these profile reports, and we tried to say most of it in the Usage Notes link at the top of the report. Here is a (slightly edited) excerpt: These reports represent the Missouri Census Data Center's attempt to distill the most frequently accessed data items from the Census Bureau's American Community Survey summary data products. American FactFinder web site users will be familiar with the ACS-based Data Profile reports on that site. These (MCDC) reports obviously are modeled after those Bureau products. (The source of most of the data used in these reports come from the xls files with Data Profiles data distributed by the Census Bureau.) But these profiles do differ in significant ways, in terms of both form and content. Some key differences:

    1. The MCDC profiles allow the user to select up to 4 geographic areas and will display the data for those areas side by side to facilitate comparison.

    2. Statistical reliability of the data are displayed here using a 3-tiered font weighting scheme with MOE-based values (relative MOE's and confidence intervals for counts; MOE values for Percents) accessible by holding the mouse over any data item on the report for 1 second. (See details, below).

    3. You can choose to view multiple profiles at once here. You can only display one Bureau profile at a time (i.e. Social, Economic, etc.)

    4. The data used in these reports are stored in datasets that can be accessed and downloaded (using our Dexter web extraction module). You can easily access these data for every geographic area in the country in a single query. Profiles on the Bureau web site only provide access to the data one geographic area at a time.

    5. These tables provide links to dynamically generated color charts for visualizing the data in a table.

    6. "Drill down" links are provided to allow viewing of detailed "parent" tables which contain (usually) more detailed data that what are shown here

    Here is a "close up" view of a portion of the Economic Profile portion of the report showing a table of household income distribution for the two cities in our report. Columbia is over twice as large as Jefferson City so you might expect less sampling errors in the larger town.

    This illustrates the use of fonts to indicate statistical reliability (bullet item 3 in the excerpt above) without sacrificing any valuable screen-space. Focus on the Jefferson City column of numbers. Of the ten income interval counts ("Less than $10,000" thru "$200,000 or more") we see that only the $50,000 to $74,999 interval is displayed using a bold font, while the entry for the last interval is barely readable due a very light font. This is quick and easy visual way of warning the user that the 240 estimate of households with the highest income level is not very statistically reliable. If the user places the cursor over the 240 value in the report the program will display   +/- 47.5% (126,234)    which reports the relative Margin of Error (i.e. the MOE as a percent of the estimate) followed by the confidence interval. There is a 90% chance that the true count is somewhere between 126 and 234, which is a rather large grain of salt. Details of how this works are provided on the Usage Notes page.
    The item after next #5) describes a companion application that generates ACS Trend reports containing similar data but for different time periods.

  4. Access ACS Data as Profiles on Census Bureau Web Site. (All users.) We have to admit to an obvious bias in terms of which ACS Profiles web site/application we prefer. It comes as a result of our looking at what the Bureau did with their profiles and then designing ours to serve as an alternative that kept what we liked about theirs and adding lots of stuff we thought would make it better. Of course, the thing that we can never have to match that the AFF site has is the Census Bureau imprimatur. Their site is official, it will always certainly be there and the data will almost never contain an error. Our site is not official, will be there as long as our state funding holds out and may occasionally contain an error, especially in the first few days of a new release.

    Access the Bureau's Data Profiles by starting at the American FactFinder site, the Data Sets options with American Community Survey selected and whichever year/period you would like. Keep in mind that if you choose the 1-year period instead of the 3-year period you will have many fewer geographic areas to choose from. On the other hand, the 3-year data are not as timely. Once you made your choice (such as the 2008 vintage and the 2006-2008 3-year Estimates as the specific data set all you have to do to initiate access to the Data Profiles is to choose that option from the set of options in the gray box on the right of the screen:

    At this point it becomes a very straightforward process to get to the profiles, at least if you have ever used American FactFinder (AFF). You get to choose a single geographic area (this is perhaps our largest gripe with the Bureau's profile tool, the fact that you can only choose a single geography at a time). The Bureau's Social profile is always displayed first, even if all you really want is the Economic profile so you can see the poverty statistics. It is easy to choose the Economic Profile after the Social Profile has displayed.

    These profiles are well formatted and contain extensive footnotes. The latter is sometimes helpful but if you want to print the same profile a lot, it can become a bit of a paper-waster. There is a special Narrative Profile, where they put "highlights" into regular English and throw in some bar charts. We are not overly impressed but they are popular among some users.

  5. Trend Reports/Comparison Tables. (All users). The trend reports that many or most people would most like to see is where we look at data from the 2000 census and compare that to the latest data from the ACS. But that we do not have, and perhaps never will. There are many issues regarding comparability of data collected from these two surveys (see item 7). So what that leaves us with are trends within the ACS data based upon different time periods. There is a general rule of thumb that prohibits comparing multi-year period figures where the two periods overlap (at least for the sake of detecting any trend). If you accept that limitation then the only trends we have to date (2010) are for single-year data. (We will not be able to do trends using 3-year period estimates until we have two overlapping 3-year periods. That will not be the case until they release the 2008-2010 period estimates in late 2011. For now, you can access the Census Bureau's Comparison Profile products (which only appear on the product menu when you have selected a single-year data resource) or the MCDC's ACS Trends dynamic report generator. This application is a companion to the MCDC's ACS Profiles application (see item 3 in this document). It only allows you to select a single geography and (for now) only those large enough (65,000+) to have single-year data. Here is a snapshot of a portion of an ACS Trends report:
    The easiest way to access the ACS Trends report is via the link to its Main Menu page which appears just below the ACS Profiles link in the Quick Links box of most MCDC web pages:

Continue with second page (containing five more things to know and do.)