Office of Immigration Statistics

OFFICE OF STRATEGY, POLICY, AND PLANS Draft

Southwest Border Migrant Encounter 

Projections

October 2023

Office of Homeland Security Statistics/Migration Analysis Center

Science and Technology Directorate/MMI
OHSS SWB ENCOUNTER PROJECTIONS

1

• The Office of Homeland Security Statistics (OHSS) runs the enterprise-wide 

Southwest border migrant encounter projections for DHS. A monthly interagency 

working group meets to discuss these projections.

• Projections inform operational, budgetary, and policy planning. They are also used 

in downstream modelling of other indicators of interest.

• I will present:

• Overview of Methodology

• Example Results

• Example Evaluations of Forecast Accuracy
OVERVIEW OF METHODOLOGY

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• Bayesian Structural Time Series (BSTS) model

• Separate simultaneous estimates of:

• Semi-local linear trend

• Autoregressive (AR) terms

• Seasonality (monthly dummy variables)

• Underlying drivers of migration, based on data-driven regression results, reviewing existing 

research, and discussions with DHS components

• Government of Mexico Apprehensions

• USA Unemployment

• Removals as share of T8 encounters

• Separate runs for each citizenship (top 14 plus all other) and family status group (Single Adult, 

Family Unit member, or Unaccompanied Child).

• Subject Matter Expert (SME) survey provides input on results. Additional assumptions are used to 

create planning lines.

• Diagnostic statistics (MAPE) calculated in each month.
SME SURVEY

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• Distributed each month to SMEs across DHS components, HHS, State, and USAID.

• SMEs react to statistical model results and provide input on whether to adjust the projections 

higher, lower, or to keep them as is.

• SMEs provide input on expectations for total encounters or by family type (SA, FM, UC).

• As participation in the SME survey has increased, the SME survey has begun to increase the forecast 

accuracy. 

• With monthly meetings to review results and discuss ongoing migration trends, the quality of SME input 

is improving over time.

• Going forward, we intend to continue expanding the number of respondents and maintaining the 

engagement of existing respondents.
PLANNING MODELS: FM & SA ENCOUNTERS (DAILY AVERAGE)

* Encounter projections exclude CBP One arrivals and OFO Paroles. 

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PLANNING MODELS: UC & UC OTM ENCOUNTERS (DAILY AVERAGE)

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* Encounter projections exclude CBP One arrivals and OFO Paroles. 
SHORT-TERM PROJECTIONS: EVALUATION

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• Evaluation statistics are calculated on a rolling basis to evaluate model performance

• Evaluation statistics include: Median Percent Error and Median Absolute Percent Error (Median APE).1

• Diagnostics allow us to identify sub-groups with the most room for improvement and test model adjustments before 

making changes.

o Example: OHSS identified CHNV as countries where models needed improvement. In January, OHSS removed the trend component 

from the models for these four countries. This has improved forecast accuracy.

1-

Month

3-

Month

6-

Month

Median Percent Error, Full 23 

Months

-1% 2% -2%

Median APE, Full 23 Months 8% 11% 18%

Median APE, Last 12 Months 11% 17% 15%

1. Medians instead of means are used because the 

arithmetic mean of the percent error is not as valid 

when dealing with evaluations of population forecasts 

(Moreno et al. 2013; Tayman & Swanson, 1999; Fildes, 

1992)
THANK YOU

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Justin Schon, PhD

Office of Homeland Security Statistics, DHS

justin.schon@hq.dhs.gov

Nadwa Mossaad, PhD

Office of Homeland Security Statistics, DHS

nadwa.mossad@hq.dhs.gov

Douglas Baals, PhD

Applied Research Associates

douglas.baals@associates.dhs.gov

Link to OHSS Products:

https://www.dhs.gov/immigration-statistics