Methodology Changes in 2003

	Population controls that reflect the results of the 2000 decennial 
census are used in the CPS/HVS estimation process for the first time in 
the first quarter 2003.  This change has a slight effect on vacancy and 
homeownership rates, as described below.  As a final additional step in 
our estimation process, the estimates are now controlled to independent 
housing counts used for the first time in order to produce a more 
accurate estimate of housing units.  This should make the CPS/HVS 
estimates of housing units more consistent with other Census Bureau 
housing surveys.  The new housing controls will affect the count of all 
housing units in the sense that both occupied and vacant units will be 
ratio estimated to the new control total.  Vacancy rates and homeownership 
rates are not be affected by this change.
	The CPS/HVS began computing first-stage factors (used for weighting 
purposes) based on year-round and seasonal counts of housing units from 
the 2000 decennial census, beginning in the first quarter 2003.  From 1980 
to 2002, the CPS/HVS first-stage factors were based on year-round estimates 
only.   We believe that this improves our counts of year-round and seasonal 
units. 
	The shift from 1990-based to 2000-based population controls (including 
the weighting revision) had a very slight effect on vacancy rates and 
homeownership rates.  Research has shown that the new 2000-based controls 
dropped the rental vacancy rate in the first quarter 2002 from 9.14 percent 
to 9.08 percent---a difference of less than 1/10 of one percent.  The 
homeowner vacancy rate was revised from 1.67 percent to 1.65 percent, while 
the homeownership rate was revised from 67.82 percent to 67.81 percent. 
	The questions on race on the CPS are modified beginning in the first 
quarter 2003 to comply with the revised standards for federal statistical 
agencies.  Respondents may now select more than one race.  The Hispanic/
Nonhispanic origin question continues to be asked separately.


 INTRODUCTION OF COMPUTER ASSISTED SURVEY COLLECTION (CASIC) AND REWEIGHTING 
CURRENT POPULATION SURVEY/Housing Vacancies and Homeownership (CPS/HVS)�BASED ON THE 1990 CENSUS

	Major changes related to the Current Population Survey/Housing Vacancy 
Survey (CPS/HVS) were effective beginning with the first quarter 1994 data.  
First, a new weighting procedure was implemented based on the 1990 decennial 
census.  The 1990-based weighting produces, on average, estimates of the total 
housing inventory that are about 0.1 percent lower than the 1980-based weighting.  
Generally, the vacancy rates were only minimally affected, while the homeownership 
rate was about one-half of a percentage point lower with the new weighting procedures.  
	A second change is that the CPS/HVS became a totally computerized survey with 
the implementation of the Computer Assisted Survey Information Collection (CASIC).  
The CASIC tools consist of state-of-the-art computer-assisted modules for data 
collection and processing.  Although the concepts, definitions, and questionnaire 
items remain the same, the shift to CASIC may affect vacancy rates and homeownership 
rates.  We are unable to determine the quantitative effects of the use of CASIC on 
the vacancy and homeownership rates.  Data users should use caution when comparing 
data for 1994 and later with earlier data.
	Beginning the second quarter of 1999, a change was made in the way data for 
housing units in structure are collected.  In the past, there was one category to 
show 1-unit in structure.  Now that has been broken into two categories: 1-unit 
attached and 1-unit detached.


SOURCE OF DATA 
 
	The estimates presented in this report are based on data obtained from two 
surveys conducted by the Bureau of the Census. Data concerning vacancy rates 
and tenure of occupied housing units are from the monthly sample of the Current 
Population Survey (CPS).  Characteristics of occupied housing units in table 3 
are from the American Housing Survey (AHS). 


CPS AND AHS DESIGNS 
 
	Since the inception of the CPS in 1940, the sample has been redesigned 
several times to upgrade the quality and reliability of the data and to meet 
changing data needs.  Beginning in April 1994, the current design was phased 
in through a series of changes that were completed in July 1995.  
	The CPS/HVS sample is selected from a frame based on the 1990 census and 
is spread over 754 sample areas, which represent 2,007 geographic areas in 
the United States.  Due to the new sample drawn from the 1990 census, 
metropolitan/nonmetropolitan data published in 1995 and later are not directly 
comparable to data for 1994 and earlier.
	Beginning in the first quarter 1986, vacant seasonal mobile homes were 
included in the count of vacant seasonal units.  This change resulted in a 
12 percent increase in the number of vacant seasonal housing units.  
	Beginning with the first quarter 2002 Housing Vacancy Report, the size of 
the CPS/HVS sample increased to approximately 72,000 housing units.  This 
expansion was one of the Census Bureau's plans to meet the requirements of the 
State Children's Health Insurance Program (SCHIP) legislation.  Of the 72,000 
housing units contained in the CPS/HVS sample, approximately 61,200 are eligible 
for interview each month; of this number, 3,900 occupied units, on the average, 
are visited but interviews are not obtained because occupants are not found at 
home after repeated calls or are unavailable for some other reason.  In addition 
to the 61,200, there are also about 10,800 sample units in an average month which 
are visited but are found to be vacant or otherwise not to be interviewed.  About 
half of the 10,800 are vacant and interviewed for the HVS.   
	The CPS estimation procedure for occupied units involves the inflation of the 
weighted sample results to independent estimates of the total civilian 
noninstitutional population of the United States by age, race, sex, and Hispanic/
non-Hispanic categories. These independent estimates are based on statistics 
from the decennial censuses of population; statistics on births, deaths, 
immigration, and emigration; and statistics on the strength of the Armed Forces.
	The HVS estimation procedure for vacant units is similar to that used for 
occupied units.  Weighted sample results are adjusted at the state level using 
2000 census vacant counts.  A second adjustment inflates these results based on 
the CPS coverage of occupied units by geographic areas.  As a final step for 
both the CPS and HVS, all housing unit counts are adjusted to reflect independent 
housing control totals.  This change is effective, beginning in the first quarter 2003.
	Data shown in all tables (except table 3) on vacancy rates and tenure of 
occupied units for the first quarter 2003 are from the CPS/HVS and are averaged 
for the three months, January, February, and March 2003.  The data concerning the 
distribution of characteristics for occupied housing units, shown in table 3, are 
obtained primarily from the AHS national sample.  Distributions of characteristics 
of occupied housing units from the AHS estimates are applied to CPS current housing 
inventory independent estimates to obtain the characteristics of occupied housing 
units used in this report.  The Survey of Construction (SOC) and the Consumer Price 
Index also are used to improve estimates of the rent distribution.  
	The 2001 AHS sample is spread over 394 sample areas comprising 878 counties and 
independent cities with coverage in each of the 50 States and the District of Columbia.  
Of the 55,800 housing units both occupied and vacant contained in the AHS sample, 
48,300 were interviewed and 5,400 were classified as
 "Type A noninterviews" for various reasons. 2,100 units were visited but were not 
eligible to be interviewed for the purposes of AHS. A detailed description of the 
AHS sample design and estimation procedure can be found in the H-150 report for 2001.  



COMPARABILITY WITH CENSUS OF HOUSING DATA 

	Most of the concepts and definitions are the same for items that appear in both 
the 1980 and 1990 censuses and the Housing Vacancies and Homeownership.  However, there is one 
minor difference in the housing unit definition between the CPS/HVS and the 1980 
and 1990 decennial censuses.  The difference is that, in the CPS/HVS prior to 1983, 
living arrangements containing five or more persons, not related to the person in 
charge, were classified as group quarters; for the 1980 and 1990 census, the 
requirement was raised to nine or more persons not related to the person in charge.  
There were some differences in what has been counted as housing units between the 
earlier censuses and the CPS/HVS.  Descriptions of the differences between earlier 
censuses and the HVS appear in the 1985 and earlier reports of this series. 
	Prior to the first quarter 1990, there were significant differences between the 
CPS/HVS and the decennial censuses.  The 1980 and 1990 decennial censuses included 
vacant mobile homes as housing units, whereas prior to 1986 the CPS/HVS did not.  
However, beginning in the first quarter 1986, vacant seasonal mobile homes were 
counted as housing units in the CPS/HVS.  In addition, year-round vacant mobile 
homes were counted as housing units, beginning in the first quarter 1990 in the 
CPS/HVS.  Another difference in the housing unit definition between the CPS/HVS 
(prior to 1986) and the 1980 and 1990 censuses was that the CPS/HVS required units 
to be separate living quarters and have direct access or have complete kitchen 
facilities.  For the 1980 and 1990 decennial censuses, the complete kitchen facilities 
alternative was dropped with direct access required of all units.  However, beginning 
in 1990, the CPS/HVS requirement for complete kitchen facilities was dropped with 
direct access required of all units.  Thus, the earlier definitional differences were 
eliminated.  
	In addition, there are differences between the methodologies used to collect data 
for the CPS/HVS and the censuses.  These differences include interviewing procedures, 
staff experience and training; differences in processing procedures and sample 
designs; the sampling variability associated with the CPS/HVS and the sample data 
from the census; and the non-sampling errors associated with the CPS/HVS and census 
data. 
	Research has shown that the CPS/HVS and the 1990 census produced significant 
differences for vacancy characteristics.  The rental vacancy rate from the April 1990 
census was 8.5 percent, whereas, the CPS/HVS reported the rental vacancy rate of 7.2 
percent for the first half of 1990.  The April 1990 census had a homeowner vacancy 
rate of 2.1 percent, while the CPS/HVS had a vacancy rate of approximately 1.7 percent 
for the first half of 1990.  For occupied housing, the April 1990 census produced a 
homeownership rate of 64.2 percent, while for the first half of 1990 the CPS/HVS 
produced a rate of 63.9 percent. These differences illustrate that, for these 
characteristics as well as others, caution should be used when making comparisons 
between the 1990 census and the CPS/HVS. 
	Further research has shown that the CPS/HVS and the 2000 census produced significant 
differences for vacancy characteristics.  The rental vacancy rate from the April 2000 
census was 6.8 percent, whereas the CPS/HVS reported the rental vacancy rate of 7.9 
percent for the first half of 2000.  The April 2000 census had a homeowner vacancy 
rate of 1.7 percent, while the CPS/HVS had a vacancy rate of approximately 1.5 percent 
for the first half of 2000.  For occupied housing, the April 2000 census produced a 
homeownership rate of 66.2 percent, while for the first half of 2000, the CPS/HVS 
produced a rate of 67.2 percent.  These differences illustrate that, for these 
characteristics as well as others, caution should be used when making comparisons 
between the 2000 census and the CPS/HVS.	
 


COMPARABILITY WITH EARLIER DATA 
 
	As stated earlier in this report, beginning with the first quarter 1994 new 
weighting procedures based on the 1990 decennial census were implemented.  In 
addition, the survey data collection procedures became totally computerized.  
Caution should be used when comparing current data with unrevised data prior to 1994.
	In the fourth quarter 1989, new edit procedures were implemented in the 
Current Population Survey/Housing Vacancies and Homeownership (CPS/HVS).  These new procedures 
were used to allocate cases that would have been classified as "not reported" 
under previous procedures.  
	In the first quarter 1990, year-round vacant mobile homes were included for 
the first time as part of the year-round vacant count of housing units.  This 
change was made to make the composition of the housing unit inventory for the 
CPS/HVS similar to the decennial census and other surveys, which count all mobile 
homes as housing units when occupied or vacant (available for occupancy on the 
site).  Research has shown that the inclusion of vacant mobile homes increased 
the vacancy rate significantly in some cases.  We have revised 1989 data in this 
report to reflect all changes.  Caution should be used when comparing data from 
1990 or later with unrevised data prior to 1990.
	In addition to the design and estimation changes mentioned in the previous 
section, caution should be used in comparing data for 1980 and beyond in this 
report with data from 1979 and earlier years. Starting with the first quarter 
1980, several changes were implemented in the survey to improve the reliability 
of the data presented.  These included adding a supplemental sample, refining the 
estimation procedures, and changing the source of occupied characteristics from 
the Quarterly Housing Survey to the AHS. 
	Although the above mentioned changes have resulted in more reliable estimates, 
data for 1980 and later in this report are not completely comparable to data for 
the fourth quarter 1979 and previous quarters, as published in Housing Vacancies 
reports, series H-111, Nos. 1 to 79-Q4.  Furthermore, unrevised data prior to 1990 
is not completely comparable to 1990 data and beyond, due to the inclusion of 
year-round vacant mobile homes, beginning in the first quarter 1990.  Thus, 
particular caution should be observed in drawing conclusions about trends that 
extend from before 1980 to 1980 and beyond, and also trends from before 1990 to 
1990 and later.  For comparative purposes, 1979 data in this report have been 
revised to incorporate all changes made in 1980, and 1989 data have been revised 
to incorporate all changes made in 1990. Unrevised 1989 and 1979  data are provided 
to show the magnitude of the various changes.  


VACANCY RATES FOR CHARACTERISTICS IN TABLE 3 
 
	Vacancy rates in table 3 are based in part on forecasts of occupied housing 
units.  These forecasts are periodically revised to incorporate more recent data 
and improved forecasting procedures.  Beginning in the first quarter 2003, 
table 3 is based on data from the 2001 AHS.  The 2002 data shown in table 3 have 
been revised to reflect this change.

	For the occupied unit forecasts for the monthly rent categories, we update 
the AHS data quarterly to reflect the rise in the cost of renting through the use 
of the residential rent index, and the latest available asking rent data for newly 
constructed rental units.  


CAUTION IN USING SEASONAL VACANT DATA 

	Analysis of seasonal vacant data prior to the first quarter 1987 has shown 
that estimates for these characteristics have been underestimated by approximately 
28 percent.  The estimates beginning with the first quarter 1987 are adjusted to reflect this.  



ACCURACY OF THE ESTIMATES 
 
	Since the CPS/HVS estimates are based on a sample, they may differ somewhat from 
the figures that would have been obtained if a complete census had been taken using 
the same questionnaires, instructions, and enumerators.  There are two types of 
errors possible in an estimate based on a sample survey:  sampling and non-sampling.  
The accuracy of a survey result depends on both types of errors, but the full extent 
of the non-sampling error is unknown.  Consequently, particular care should be exercised 
in the interpretation of figures based on a relatively small number of cases or on 
small differences between estimates.  The standard errors provided for the CPS/HVS 
estimates primarily indicate the magnitude of the sampling error.  They also partially 
measure the effect of some non-sampling errors in responses and enumeration; but do not 
measure any systematic biases in the data.  (Bias is the difference averaged over all 
possible samples, between the estimate and the desired value.) 




NON-SAMPLING VARIABILITY 
 
	Nonsampling errors can be attributed to many sources, e.g., inability to obtain 
information about all cases in the sample, definitional difficulties, differences in 
the interpretation of questions, inability or unwillingness on the part of respondents 
to provide correct information, inability to recall information, errors made in 
collection such as recording or coding the data, errors made in processing the data, 
errors made in estimating values for missing data, and failure to represent all units 
with the sample (undercoverage).  Undercoverage in the CPS/HVS results from missed 
housing units and misclassifying housing units. Ratio estimation to independent controls, 
as described previously, partially corrects for the bias due to survey undercoverage.  
However, biases exist in the estimates to the extent that missed households have different 
characteristics than interviewed households.  


SAMPLING VARIABILITY 
 
	The standard errors shown in the tables are primarily measures of sampling variability, 
that is, of the variations that occurred by chance because a sample rather than the entire 
population was surveyed.  The sample estimate and its standard error enable one to construct 
confidence intervals; ranges that would include the average results of all possible samples 
with a known probability.  For example, if all possible samples were selected, each of 
these being surveyed under essentially the same general conditions and using the same sample 
design, and if an estimate and its standard error were calculated from each sample, then 
approximately 90-percent of the intervals from 1.6 standard errors below the estimate to 
1.6 standard errors above the estimate would include the average result of all possible 
samples. 
	The average estimate derived from all possible samples is or is not contained in any 
particular computed interval.  However, for a particular sample, one can say with specified 
confidence that the average estimate derived from all possible samples is included in the 
confidence interval. 
	Standard errors may also be used to perform hypothesis testing, a procedure for 
distinguishing between population parameters using sample estimates.  The most common 
types of hypotheses appearing in this report are:  (1) the population parameters are 
identical, and, (2) the population parameters are different.  An example of this would 
be comparing the vacancy rate in MAs versus the vacancy rate outside MAs.  Tests may be 
performed at various levels of significance, where a level of significance is the 
probability of concluding that the characteristics are different when, in fact, they are 
identical. 
	To perform the most common test, let x and y be sample estimates for two characteristics 
of interest.  Let the standard error on the difference x-y be SEDIFF.  If the 
ratio R = (x-y)/SEDIFF is between -1.6 and +1.6, no conclusion about the difference between 
the characteristics is justified at the 0.10 level of significance.  If, on the other hand, 
this ratio is smaller than -1.6 or larger than +1.6, the observed difference is significant 
at the 0.10 level.  In this event, it is a commonly accepted practice to say that the 
characteristics are different. Of course, sometimes this conclusion will be wrong.  When 
the characteristics are, in fact, the same, there is a 10 percent chance of concluding that 
they are different.  All statements of comparison in the text have passed a hypothesis test 
at the 0.10 level of significance or better.  This means that, for most differences cited 
in the text, the estimated difference between characteristics is greater than 1.6 times 
the standard error of the difference. 
	Comparisons of characteristics of the vacancies for the first quarter 1990, 
(which include year-round vacant mobile homes as part of the year-round vacant housing 
inventory for the first time) with previous unrevised quarters reveal significant 
differences in some cases.  Thus caution should be used when comparing current data with 
unrevised data prior to 1990.
 
<strong>ILLUSTRATION OF THE USE OF TABLES OF STANDARD ERRORS</strong> 
 
	Standard errors are used to: 1) measure the accuracy of the survey estimates, and 
2) draw inferences from the survey data.  For example, Table 10 of this report shows that 
3.0 percent of all housing units are vacant and available for rent.  Table A-1 shows the 
standard error of this estimate to be approximately 0.1 percentage points.  Consequently, 
the 90-percent confidence interval as shown by these data is from 2.8 to 3.2, i.e., the 
interval 3.0 + (1.6 x 0.1) percentage points.  Thus, one can say with about 90-percent 
confidence that the average rental vacancy rate derived from all possible samples is 
included in this confidence interval.  Statements about differences are made only when 
the 90-percent confidence interval on the estimated difference does not include zero.  
The 90-percent confidence intervals are shown in the text for selected items.  The 
standard errors for other figures in this report are given in the tables. In addition 
to sampling error, the figures in this report, both the estimates and their standard 
errors, are also subject to rounding error.


Table A-1.  Standard Errors of Percentages in Tables 10 and 11:  First Quarter 2003




                                  Vacant for-rent units as a
                                  percent of all housing units


                                                         Standard
Area                               Standard    Differ-   error on
                           Rate      error     ence\1   difference


United States..........       3.0        0.1        0.1        0.1
  Inside MAs...........       3.2        0.1        0.1        0.1
  Outside MAs..........       2.2        0.1        0.1        0.2

 Northeast.............       2.1        0.1        0.1        0.2
 Midwest...............       2.7        0.1        (z)        0.2
 South.................       3.7        0.1        0.2        0.1
 West..................       2.7        0.1        0.1        0.2



                                  Vacant for-sale-only units as a
                                  percent of all housing units

                                                         Standard
Area                               Standard    Differ-   error on
                           Rate      error     ence\1   difference


United States..........       1.0        (z)        (z)        (z)
  Inside MAs...........       1.0        (z)        (z)        (z)
  Outside MAs..........       1.2        0.1        (z)        0.1

 Northeast.............       0.6        0.1       -0.1        0.1
 Midwest...............       1.1        0.1        (z)        0.1
 South.................       1.2        0.1        0.1        0.1
 West..................       0.9        0.1        0.1        0.1

(z) Less than 0.05.       - Represents zero.
\1 Represents difference in first quarter 2003 and revised first quarter 2002 rates.