Most information on Border Patrol activities along the border come from data that has already been aggregated and compiled by Customs and Border Protection (CBP), Border Patrol’s parent agency. We acquired the Border Patrol microdata for every apprehension on the Southwest Border from September 1, 2014, through August 31, 2015. That period adds one month from the end of the 2014 fiscal year and chops off the last month of the 2015 fiscal year. The microdata allow us to answer specific questions about Border Patrol apprehensions that aren’t otherwise displayed in tables by CBP. This microdata identifies an individual’s time and date of apprehension and release, which allows us back out how long they were held in Border Patrol custody.
There is wide variation between the number of hours that illegal immigrants apprehended by Border Patrol on the SW border stay in detention based on the region of the world where they are from (Table 1). Caribbean illegal immigrants spend an average of 61 hours in detention, but there were only 561 of them detained in 2015.
But the most striking numbers from Table 1 is the standard deviation column. The standard deviation measures the dispersal of the data points. If the standard deviation is low, then the data points are all clustered about the mean. If the standard deviation is high, the data points are spread out over a wide period. The standard deviation for the number of hours spent in detention for Central Americans and Mexicans is about two to three times greater than the next highest standard deviation, respectively. This is likely because of the large number of asylum claims made by Central Americans and Mexicans in 2015.
Table 1
Hours Detained on SW Border by Country of Origin
| Region of Origin | Average Number of Hours | Standard Deviation | Number of Illegal Immigrants |
| Caribbean | 61.06 | 40.92 | 561 |
| South America | 47.51 | 32.25 | 4,548 |
| Central America | 44.13 | 105.53 | 130,156 |
| Oceania | 37.87 | 30.55 | 3 |
| Asia | 37.61 | 23.63 | 4,309 |
| MENA | 37.10 | 29.33 | 151 |
| Europe/Canada | 36.54 | 53.17 | 529 |
| Mexico | 35.65 | 144.89 | 186,547 |
| Africa | 23.34 | 28.05 | 56 |
| Other/Unknown | 14.72 | 12.36 | 6 |
| All | 39.26 | 128.31 | 326,866 |
Source: CBP Microdata.
Table 2 shows how many hours immigrants spend in detention by the border sector where Border Patrol apprehended them. There’s no correlation between the number of hours an illegal immigrant is held for with the border sector in which they were apprehended, even controlling for the number of Border Patrol agents by sector.
Table 2
Hours Detained on SW Border by Border Region of Apprehension
| Border Sector | Average Number of Hours | Standard Deviation | Number of Illegal Immigrants |
| Laredo | 65.97 | 72.13 | 35,509 |
| Big Bend | 52.71 | 236.44 | 4,492 |
| Rio Grande | 41.06 | 86.95 | 145,493 |
| San Diego | 35.00 | 89.30 | 26,415 |
| Del Rio | 31.07 | 313.42 | 18,294 |
| Yuma | 29.81 | 118.89 | 6,633 |
| El Paso | 29.80 | 261.71 | 14,046 |
| El Centro | 28.88 | 66.67 | 12,615 |
| Tucson | 28.52 | 104.15 | 63,369 |
| All | 39.26 | 128.31 | 326,866 |
Source: CBP Microdata.
Altogether, illegal immigrants apprehended along the SW border spent over 12.8 million hours in detention in 2015 – equal to about 1,464 years of detention. If the daily cost of maintaining a guarded bed in Immigration and Customs Enforcement (ICE) detention facilities is the same as the cost for those detained on the SW border, then it cost over $50 million in 2015 to detain those 326,866 people for more than half a million days.