June 14, 2011

V. Methodology

The data provided in response to the original Freedom of Information Act (FOIA) request arrived from ICE on a single data disc and contained 5,061,411 comma-separated value records, comprising 1.16 GB of data.

ICE did not provide a data key or code book for deciphering the data. After exploring the database, researchers determined that of the 18 included variables, five variables were either completely empty or contained major data entry flaws. For example, the variable “Apprehension Date” has a large percentage of entries (over 120,000 people) with the same date of apprehension: 1/1/2001. This is clearly a result of a data management error such as a wrongly labeled bulk import.

Researchers found that each row of data was based upon a single action (transfer or deportation or other release) or segment of someone’s detention, not a single person’s history. After further analysis, researchers were able to use consistencies among several variables to determine the ordering of the database. With the ordering of the database known, we were able isolate individuals’ histories within ICE detention by identifying the individual non-citizen that corresponded to each row of data.

Our analysis relied on descriptive statistics, including frequencies and cross-tabulations.  Distance estimates were developed by determining latitudes and longitudes of each detention facility and computing the distance between each facility. Cost estimates were developed using data provided by the US Marshals Service on cost per flight hour per seat for transfers conducted by the Justice Prisoner and Alien Transportation System (JPATS). The US Marshals Service provided six years of estimates for flights using different sizes of airplane frames. We averaged these estimates to produce an average per transfer cost.

The last date included in the database was May 25, 2010, which corresponds to 64 percent of fiscal year 2010. Therefore, we developed estimates for the remainder of FY2010.  Estimated FY2010 will be labeled “Estimated.” Because the volume of ICE actions follows an annual pattern, with drops in enforcement actions around the fiscal year changeover, we did not use a linear rate for estimates. Rather, estimates were developed by using rate ratios determined using data from 2007 through 2009 in an attempt to improve accuracy. These ratios compared the volume of ICE detentions, transfers, and deportations from October through April to May through September. A ratio of 1:1 would mean that the volume from October to April would equal the volume from May to September. The averaged ratio of the previous three fiscal years was applied to the October through April 2010 data to estimate the aggregate sums for the remainder of 2010.

For cost estimates, two formulas were used to calculate the approximate cost per transferred detainee:

  • For each ICE detainee transferred 475 miles or more, we assumed air travel and calculated the cost as:[37] cost = [(C / 525) x $373.88 ].
  • For each detainee transferred under 475 miles, the following formula was applied:[38]
  • cost = [(mileage traveled / 60) x $32 per hour for 2 guards] + (mileage traveled x $0.50 per mile).

Data that the Department of Homeland Security provided has not been altered for our analysis.  Any errors within the dataset, including user-generated errors such as mislabeling in data entry, would have occurred before the dataset was received. Because original files on each deportee are not accessible, it is impossible to double check the data entry for errors.  Therefore the analysis uses data that ICE provided, regardless of any potential errors.

[37]Formula explanation:

C = distance (over 475 miles) traveled by each detainee. The 475-mile cut off is based on a comparison between the Internal Revenue Service (IRS) standard mileage rate for automobiles in FY 2010, which was $0.50 per mile (http://www.irs.gov/newsroom/article/0,,id=216048,00.html), and flights on commercial carriers between a variety of destinations, to determine at what distance a prudent decision-maker might choose to transport detainees by plane as opposed to over land (see table below). Some of the flight costs were based on rates that included one stop-over, since the US Marshalls described using stopovers while transporting immigrant detainees. Email from Steve Blando, US Marshals Service Headquarters, to Human Rights Watch, May 30, 2008 (“On average an alien may move 1.4 times before reaching final destination”).


Over land

By commercial carrier

Philadelphia (77 miles)



Washington, D.C. (197 miles)



Richmond, VA (283 miles)



Detroit, MI (474 miles)



Charlotte, NC (526 miles)



Atlanta, GA (735 miles)



New Orleans, LA (1,163 miles)




525 = number of miles traveled per flight hour. (The “typical cruise speed” of a Boeing 737 at 35,000 feet is about 525 mph). The Boeing Company, “Commercial Airplanes: 737 Family,” http://www.boeing.com/commercial/737family/pf/pf_800tech.html (accessed May 11, 2011).

$373.88 = price per flight hour per seat charged by Justice Prisoner and Alien Transportation Service (JPATS) of the US Marshals Service to ICE, on average between fiscal years 2006 and 2011 and among all types of aircraft frame. Letter from William E. Bordley, Associate General Counsel/FOIPA Officer, US Department of Justice, United States Marshals Service, to Human Rights Watch, regarding freedom of information/privacy act request no. 2011USMS17132, March 3, 2011.

[38]The formula is a rough estimate based on the following assumptions. A transfer requires the presence of at least two guards. In 2007 guards were compensated at a rate of $16 per hour. See Amendment of Solicitation/Modification of Contract between ICE and Lincoln County, Troy, Missouri, “The purpose of this modification is to add Article XVIII (Guard/Transportation Services) to this agreement,” August 23, 2007 (“At least two (2) qualified law enforcement or correctional officer personnel employed by the Service Provider under their policies, procedures and practices will perform services.”). In addition, billing for transportation costs is based on the IRS standard mileage rate for automobiles of $0.50 per mile in FY 2010 (http://www.irs.gov/newsroom/article/0,,id=216048,00.html). Depending on the number of detainees transported in a transfer, more than two guards may be required. In addition, hourly rates for guards may have increased since 2007. Therefore, we believe that these estimates for ground transportation costs are conservative.