The Use of ZIP Code Data in Jury Selection

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Article Published in Westchester County Bar Association – Bar Journal

Volume 34, Number 2; Fall/Winter 2007

By Gary R. Giewat, Ph.D.*


The goal of jury selection is to minimize the likelihood of unfavorable and potentially biased jurors being seated on the jury panel. In jury selection, attorneys strive to gain as much information as possible from jurors in order to execute cause and peremptory challenges. Various formats of jury selection result in differing degrees of evaluation of prospective jurors. For instance, an optimal situation would involve pretrial research being conducted to prepare a juror profile, having supplemental juror questionnaires completed by members of the venire, the completed questionnaires being reviewed prior to trial, and the judge permitting attorneys to conduct voir-dire. In contrast, jury selection is least comprehensive in situations where the judge conducts limited voir-dire and there is no attorney questioning or supplemental jury questionnaire involved — the situation found most often in Federal Court.


The purpose of this article is to outline ways in which attorneys and consultants can supplement voir-dire through the use of existing data, namely that of varied aggregate demographic data that may be found in the US Census Bureau’s website. While useful, demographics alone are probably the least predictive indicators of which jurors may or may not be unfavorable. However, demographics are often inter-correlated with other factors. Certain variables may provide insight (e.g., median household income and average real estate taxes as a measure of socioeconomic status) when the trial team has some indication that a certain juror profile might be less favorable. When demographic data is paired with that obtained from voir-dire, the information converges to provide a “big picture” and affords the trial team with a higher degree of confidence in the choice of strikes. The tool for gathering this information is the prospective juror’s ZIP Code.

The Data

A ZIP Code (an acronym for zone improvement plan) is a five-digit numerical Code defined by the U.S. Postal Service to simplify and expedite mail distribution. The United States is divided into 10 large geographical areas, indicated by the first ZIP Code digit. A first digit of 0 indicates the northeast region and 9 indicates the west. The second and third digits are used to divide states; the fourth and fifth digits represent local delivery areas.1 So, how is the system used by the United States Postal Service to deliver mail useful in identifying unfavorable jurors?

The United States Census Bureau collects information about the nation’s people and its economy that may be useful in identifying favorable and unfavorable jurors on the basis of aggregate data. It is well known that demographics alone have limited predictive value, but demographic data may be used to become more familiar with the jurors. Knowing the median household income, average real estate taxes, public assistance income, etc. of the areas in which jurors reside, helps to provide some insight into their circumstances and environment. For instance, to an attorney that is not familiar with a venue such as Bronx County, New York, the general socioeconomic status of residents in ZIP Code 10464 is considerably different than residents in 10474. Determination of issues such as average real estate taxes and median household income can be found in Census data, which provides the means to view a county, a venue, by ZIP Code – data that is often provided by jurors. Although a certain ZIP Code may overlap two different counties, to some degree, the majority of ZIP Codes will be found primarily within a county.

How To Search

The US Census Bureau is found online at The starting point on the home page is the “Summary File 3 (SF3).”

At the next screen, headed “Summary File 3 (SF3),” toward the bottom of the page, click on “Data: Access to all tables and maps in American FactFinder.”

The “Summary File 3 (SF3)” dataset will be shown on the next screen. Click on “Detailed Tables,” then on the “geo within geo” tab, which allows the user to iden- tify data by ZIP Code. This brings you to a page titled “Data Sets” “Decennial” “Census 2000.” The third item on the page will be highlighted in grey: Census 2000 Summary File (SF3) – Sample Data.” To the right, click on “Detailed Tables.”

The next screen offers tabbed options. Select the “geo within geo” tab. That brings you to a series of options to select. Make your selections and click on the “Next” button to proceed.

Here the user may click on “download”, thus opening another window. In the window that opens, the default file is Comma Delimited (.csv), a good choice for managing the data in an Excel format. At the bottom of the screen, be sure to select the box that allows for downloading the descriptive data element names, and then click on “OK” to download.

The end product of these steps is to create a spreadsheet that outlines a variety of demographic data. After the data has been downloaded, the user must edit and merge the information into a final, manageable product that is user friendly: some-thing that allows for quick reference in the courtroom setting to gain more insight into a prospective juror’s background. Exactly how the data is used is left to the imagination and skill of the attorney or consultant; how the trial team has determined, a priority, which jurors it believes are least favorable. In determining which jurors have the highest priority for strikes, it might be useful to highlight those ZIP Code areas that are less favorable to the trial team.

ZIP Code data, paired with Census data, may be a valuable source of information to increase the effectiveness and thoroughness of jury selection. In summary, this involves identification of the main demographic issues of interest, gathering data from the US Census Bureau’s website, and contrasting varied demographic features with the ZIP Codes of prospective jurors.


1 2 For instance, a ZIP Code in some instances may straddle two different counties; ZIP Codes do not necessarily follow boundaries such as town or county.

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