Sample Design

2015 American Housing Survey Sample Design and Weighting
The 2015 American Housing Survey (AHS) is a longitudinal survey and has two parts: a national
and a metropolitan sample design that we refer to as AHS-N and AHS-MS, respectively. The
estimates from both AHS-N and AHS-MS will be derived from a sample of housing units
interviewed between May and September 2015. In the AHS-N sample design, sample housing
units will be interviewed every two years until a new sample is selected. For the sample of
AHS-MS, sample housing units follow a longer interviewing cycle. The U.S. Census Bureau
updates the sample by adding newly constructed housing units and units discovered through
coverage improvement efforts.
For the 2015 AHS, approximately 92,025 sample housing units will be interviewed for the AHSN sample and approximately 30,391 sample housing units will be interviewed for the AHS-MS.
AHS-N SAMPLE DESIGN
The AHS-N employes a two-stage sample design. First, the U.S. was divided into areas
consisting of counties or groups of counties and independent cities known as primary sampling
units (PSUs). The sample for AHS includes just over 500 PSUs. These PSUs cover
approximately 900 counties and independent cities with coverage in all 50 states and the District
of Columbia.
The counties of the top 85 Core Base Statistical Areas (CBSAs), according to the 2010 projected
OMB definitions, were included in the first-stage sample design with certainty. These PSUs are
known as a self-representing PSUs because they represent themselves and no other PSUs.
The Census Bureau grouped the remaining PSUs into first-stage strata and selected one PSU per
strata, proportional to the number of housing units in the PSU, to represent all PSUs in the strata.
The selected PSUs are referred to as nonself-representing PSUs because they represent
themselves and all of the other PSUs in the same strata.
Allocation of sample housing units. The initial national sample size of 52,025 was allocated to
the sample PSUs proportional to the first-stage strata HU counts from the Census 2010. For each
of the top 15 CBSAs in the U.S., we added another 3,000 sample units. The long-range plan is to
have the top 15 CBSAs as a permanent feature of the national sample design. It will mean that
the national sample design will support reasonable estimates for national estimates and for each
of the top 15 CBSAs individually. The difference between national sample size of 92,025 and
97,025(=52,025 + 3,000*15 ) is the initial sample allocated to the top 15 CBSA, as well as a
subsidized renter oversample (5,520) and a bridge sample (6,000). This overlap was not added
to the 3,000 sample sizes for the CBSAs.
Selection of sample housing units. The AHS sample within each PSU consists of the following
types of units in the sampled PSUs:



All housing units on the Census Bureau Master Address File as of 2014
Housing units in a sample of Coverage Improvement blocks

The second-stage sample design is a systematic random sample from an ordered list. A
combination of geographic variables, tenure, and the identification of housing units participating
in HUD programs was used to sort the list of HUs prior to selecting the sample.
AHS-N ESTIMATION
Each housing unit in the AHS sample represents itself and over 2,000 other units. The exact
number it represents is its “weight.” The weight was calculated in six steps and the purpose of
these steps is to minimize both sampling errors and errors from incomplete data. The description
that follows is consistent with the weighting methodology for the prior cohort interviewed from
1985 to 2013. For 2015, we plan to complete several research projects whose aim is to improve
the weighting, but may differ from this description.
The final weight is the product of the weights and factors described below and was calculated in
the order listed below. The calculation of each factor used all of the previsouly calculated
factors.
1.

Base weight. Each unit is assigned a weight to reflect its probability of selection. The
basic weight accounts for the sample selection of PSUs in the first stage and housing
units in the second stage. The base weight also accounts for any reductions or expansions
of the sample.

2.

First-stage ratio adjustment. The weights are adjusted for differences between the
number of housing units for the complete set of nonself-representing (NSR) PSUs and the
estimated number of housing units nonself-representing (NSR) PSUs where only the
sample PSUs contribute to the estimate. This can be represented as:
Number of housing units in all PSUs
of the nonself-representing PSUs
Estimated number housing units in all PSUs
of the nonself-representing PSUs
This adjustment is done separately for groups that have yet to be determined.

3.

Noninterview adjustment. An adjustment will be made for noninterviews of occupied
units. The calculations for this adjustment will not include units the Census Bureau could
not locate. The earlier weight will be multiplied by the following factor:
Interviewed units + Units not interviewed
Interviewed units
It is assumed the units missed are similar in some ways to the units interviewed for AHS.

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This adjustment is done separately within cells that are related to the propensity to
respond and the variable of interest. For 2015, research is planned to determine the best
set of variables to use in the noninterview adjustment and will be completed in 2015.
4.

Adjustment to Independent Housing Unit totals. Independent totals of housing units will
be used to adjust for known deficiencies in sampling new construction by multiplying the
earlier weight by the following factor:
Independent estimate
AHS sample estimate
This adjustment will be completed separately for groups that have yet to be determined
by planned research.
The known totals will be based on the Census Bureau's Survey of Construction and
Survey of Manufactured Home Placements. Note that final AHS figures for the
categories above are not really based on the AHS sample findings, but on the independent
sources.

5.

Adjustment to Independent Population Totals. Comparability of population estimates
among the surveys will be ensured by multiplying the earlier weight by the following
factor:
Independent estimate
AHS sample estimate
This adjustment will be completed separately for groups that have yet to be determined
by planned research.

Repetitions. The new construction and demographic adjustments will be repeated to help match
both sets of independent estimates simultaneously.
Small groups. In each step of weighting, many items were cross-classified; so some groups may
have few cases. When a group is too small (less than 30 cases) or the adjustment factor is too
extreme (greater than 2.0 for the noninterview adjustment or outside a range of 0.5 to 2.0 for the
demographic adjustment) the Census Bureau combined the group with one or more other groups
that are similar in most respects.

AHS-MS SAMPLE DESIGN
The 2015 AHS-MS sample provides information on 15 metropolitan areas interviewed as part of
the AHS. The metropolitian areas are all defined by the 2013 Office of Management and Budget
(OMB) projected definitions for CBSAs. The supplemental sample of 15 metropolitan areas
includes about 3,000 housing units each for a total of 30,391 units.
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AHS-MS ESTIMATION
Sample weights for the AHS-MS will be calculated in the same way as the national weights, but
without a first-stage ratio adjustment and without an adjustment to independent HU totals.
AHS VARIANCE ESTIMATION
Replicate weights will be calculated for both the AHS-N and AHS-MS and will be used to
calculate both the estimates provided in publications and be made available to the public. The
AHS-N replicate weights will use Balanced Repeated Replication estimate the variation due to
the selection of PSUs in the first-stage and Successive Difference Replication (SDR) to estimate
the variation due to the selection of HUs within each of the self-representing PSUs. The AHSMS replicate weights will use SDR to estimate the variation due to the selection of HUs within
each CBSA.

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