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American Community Survey: Controlling Estimates of Group

Quarters Population at the County Level

Prepared for the 2010SDC-CIC Joint Steering Committee MeetingsFebruary 23, 2010

Presented by: Michael BeaghenDepartment of CommerceU.S. Census BureauWashington, DC 20233

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Overview

• How we control ACS estimates of GQ population

• Why we don’t control ACS estimates of GQ population at the county-level

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Why Control ACS Estimates?

• Reduce coverage bias• Make ACS estimates consistent with

the Population Estimates Program (PEP) estimates

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How are Estimates of GQ Population Controlled?

Adjust total weight of sampled GQ persons to equal PEP estimates– At the state level– By seven major types of GQ

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Seven Major GQ Types Used in Controlling

– Correctional institutions – Juvenile facilities – Nursing homes– Other long-term care facilities– College dorms– Military facilities– Other non-institutional GQs

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Example of Controlling

1. PEP estimate of the population in college dorms in Big State is 11,000

2. ACS pre-controlled estimate of population in college dorms is 10,000

3. Adjust the weight of each ACS sample person in a college dorm by a factor of 1.1

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Question

• Why not control ACS estimates of GQ population at the county-level?

• Achieve consistency between ACS and PEP estimates down to county-level

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Two Possible Alternatives under Consideration

1. Adjust ACS to PEP county estimates by major type of GQ

2. Adjust ACS to PEP by total county GQ population

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Major Limitation for these Methods of GQ County Controls

• Some counties don’t have GQ sample for one or more major types of GQ which exist in the county.

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Counties With and Without ACS Sample of Major Types of GQ in 2006-2009 ACS Major Type of GQ Counties

Without ACS Sample

Counties With ACS Sample

Correctional Institutions 953 1,792

Juvenile Facilities 522 660

Nursing Homes 354 2,601

Other Long-term Care 781 551

College Dormitories 168 987

Military Facilities 180 216

Other Non-institutional 935 1,888

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Consequences of not having ACS Sample for Specific Types of GQ

• Controlling by major type of GQ requires combining types of GQ– If we don’t have sample for a type of GQ,

have to combine this type with a GQ type with sample

• Controlling by total GQ population– Combines all seven types of GQ

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Consequences Continued

• Would lead to distortions in ACS county estimates of GQ population

• Because weights of people in types of GQ in sample would be adjusted up to account for people in types of GQ not in sample

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Example of Distortion

• A county has two GQ facilities with total PEP GQ population of 220– Nursing home with 200– Juvenile facility with 20

• Juvenile facility is in ACS sample• Nursing home not in ACS sample• County-controlled ACS estimate

– 220 people in a juvenile facility

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Distortion of Estimates

• Distorts estimates of population by type of GQ

• Distorts estimates of characteristics, because people in different types of GQ have different characteristics

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Another Consideration

• PEP state estimates of GQ population are more robust than county estimates– County-level errors tend to cancel at the

state-level

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Next Steps• We are considering county-level

controls– Research is required to evaluate the

severity of distortions on ACS county and state estimates

• We are also considering very new estimation methodologies which would make controlling at the county-level less problematic

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Contact

Michael.a.beaghen@census.gov