Comparing ACS with Census Sample and Current Survey DataSome Sources for ComparisonWhat should we compare?ACS and the Decennial CensusHow do the samples compare?Sampling RatesSlide 7How does data collection compare?Slide 9What is the impact on the data?Slide 11PowerPoint PresentationSlide 13What do the estimates represent?Slide 15Weighted Census 2000 Sample and 2000 ACS Housing Units by Response WeekWhat do the Census 2000 sample estimates represent?Census 2000 Data Collection DesignWhat do the ACS estimates represent?ACS Data Collection DesignHow did the 2000 ACS and Census 2000 results compare?Comparisons with Census 2000Slide 23Slide 24Summary of National-Level Comparisons of General Demographic and Housing Characteristics (Table 1)General Demographic CharacteristicsSummary of National-Level Comparisons of Social Characteristics (Table 2)Social CharacteristicsSummary of National-Level Comparisons of Economic Characteristics (Table 3)Economic CharacteristicsSummary of National-Level Comparisons of Housing Characteristics (Table 4)Physical Housing CharacteristicsFinancial Housing CharacteristicsSummary of Reasons for DifferencesConclusionsWhat about current surveys?Comparisons with CPS & ASECComparisons with CPS and ASECSlide 39Slide 40Comparisons with American Housing Survey (AHS)Comparisons with the American Housing SurveySlide 43General Guidelines for Single-year Annual EstimatesSlide 45ACS Data ProductsIllustration of an ACS Release scheduleSlide 48Comparing ACS with Census Sample and Current Survey DataPartnership and Data Services Training Susan LoveApril 12, 2005Some Sources for ComparisonCensus long form samples in general and Census 2000 in particularCurrent Population Survey and Annual Social and Economic SupplementAmerican Housing SurveyWhat should we compare?Sampling frames and sample designData collection time frames and modesInterviewer requirementsRespondent requirementsData completenessWeighting and estimation methodsFinal results at comparable geographiesACS and the Decennial CensusHow do the samples compare?SimilaritiesSystematic samples of MAF addressesDifferential sampling rates for areas based on population sizeSampling RatesGovernmental Unit Size: Number of Occupied Housing UnitsCensus 2000 Sampling RatesACS 5-year Sampling Rates0 - 200 50.0% 50.0%201 - 800 50.0% ~35.0%801 - 1200 25.0% ~17.5%1201 - 2000 16.7% ~12.0%Over 2000 12.5% ~8.5%How do the samples compare?DifferencesACS samples every year and spreads sample over 12 months; census samples once a decade and uses the entire sample at the same time ACS subsamples for personal visit followup; court ruled against census subsamplingCensus sample estimates based on about 18 million housing units; ACS 5 year estimates based on about 11 million housing unitsHow does data collection compare?SimilaritiesPrimary method is self-response to a paper questionnaireContent is the sameHow does data collection compare?DifferencesACS nonresponse FU uses CATI and CAPI instruments; past censuses have used only paper questionnairesACS data collected only from household members; census data often collected from neighborsACS interviews conducted by experienced and well-supervised staff; census enumerations conducted by inexperienced temporary workforceWhat is the impact on the data?ACS estimates have higher sampling error –measures are released for each estimate and shown as 90% confidence limits or margins of error in every tableSimilar sampling error measures for census long form sample estimates have not been providedWhat is the impact on the data?ACS estimates have lower potential nonsampling error –Unit nonresponse: no data for a case–Item nonresponse: data missing for an item These and other measures are released on ACS’s Quality Measures website www.census.gov/acs/www/UseData/sse/index.htm11Unit Nonresponse 97.7--200296.7--200396.7--200195.191.22000ACSCensus 2000 SampleResponse Rates (100-unit nr rate)12Item Nonresponse 7.114.9Housing items - Followup5.911.5Housing items - Mail4.512.9Population items - Followup8.18.7Population items - Mail6.610.4All modes/ items2000 ACSCensus 2000 SampleSummary Allocation Rates(amount of data missing from interviews)What do the estimates represent?Most ACS estimates are said to be the average characteristics of an area over a calendar yearCensus sample estimates are often said to be characteristics of an area as of Census DayIs this so?What do the estimates represent?Both the ACS interview date and the census enumeration date play important roles ACS uses the interview date as the single reference point, or as the end of a reference period, for all data collectionThe Census 2000 sample did too, except for income, migration, and agricultural salesWeighted Census 2000 Sample and 2000 ACS Housing Units by Response Week05,000,00010,000,00015,000,00020,000,00025,000,00030,000,000147101316192225283134374043464952Interview Week in Calendar Year 2000Weighted Housing UnitsCensus 2000 Sample 2000 ACSWhat do the Census 2000 sample estimates represent?Census 2000 data collection was a sequential process of 3 operations over a 6 month periodData from these operations were processed together, weighted and tabulatedThe characteristic estimates are the sum of the peaks and valleys of the enumerations, not Census DayCensus 2000 Data Collection Design M o n th o f C e n s u s 2 0 0 0 E n u m e r a tio n M a r c h A p r il M a y J u n e J u ly A u g u s t M a il N R F U C IF UWhat do the ACS estimates represent?ACS data collection is a sequential process of 3 operations on each of 12 monthly samples over 3 month periods–All 3 operations take place every month on different sample panels, a continuous series of interviewsData collected in a calendar year are grouped by interview month; a weighting adjustment is applied to smooth overall monthly differences Summed estimates are considered the average characteristics of all areas for the calendar yearACS Data Collection Design1 9 9 9 2 0 0 0 M o n th o f In te r v ie w A C S S a m p le P a n e l N o v e m b e r D e c e m b e r J a n u a r y F e b r u a r y M a rc h A p r il M a y J u n e N o v e m b e r M a il C A T I C A P I D e c e m b e r M a il C A T I C A P I J a n u a ry M a il C A T I C A P I F e b ru a ry M a il C A T I C A P I M a rc h M a il C A T I C A P I A p ril M a il C A T I C A P I M a y M a il C A T I J u n