DESIGN FEATURES OF NCHSSURVEYS
By Iris Shimizu
Mathematical Statistician
Office of Research and Methodology, NCHS
Disclaimer: The opinions in this presentation are those of the presenter and not necessarily those of NCHS.
OUTLINE• DESIGN FEATURES OF ESTABLISHMENT
SURVEYSo SAMPLE DESIGNo DATA WEIGHTS
• FEATURES COMMON TO ALL COMPLEX SAMPLE SURVEYS
(both establishment and population surveys)
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ESTABLISHMENT SURVEYS
TARGETED ANALYSIS UNITS: • CLIENTS OF ESTABLISHMENT
• EVENTS OCCURRING AT/WITH ESTABLISHMENT
• ESTABLISHMENTS THEMSELVES
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National Health Care Survey
• National Hospital Discharge Survey• National Survey of Ambulatory Surgery• National Ambulatory Medical Care Survey• National Hospital Ambulatory Medical Care Survey• National Nursing Home Survey• National Home and Hospice Care Survey
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FEATURES
• MULTI-STAGE SAMPLING
• PRIMARY SAMPLING UNITS (PSUs)o ESTABLISHMENTSo AREAS (USED TO SAVE COSTS)
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FEATURES (CONTINUED)
• STRATIFICATIONo GEOGRAPHYo PROVIDER SPECIALTYo SIZE (INPATIENT BEDS, VISIT VOLUME)o ESTABLISHMENT TYPEo OWNERSHIP TYPE
• SELECTION WITH PROBABILITY PROPORTIONAL TO SIZE (PPS)
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FEATURES (CONTINUED)
• SAMPLING FREQUENCYo EVERY YEAR FOR PHYSICIANSo PERIODICALLY FOR OTHER
ESTABLISHMENTS BASIC SAMPLE –NEW DESIGN
UPDATES PERIODICALLY
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FEATURES (CONTINUED)
• WITHIN ESTABLISHMENT SAMPLINGo TIME SAMPLEo VISIT SAMPLE –FROM FRAME PROVIDED
BY ESTABLISHMENTo STRATIFICATIONo SYSTEMATIC RANDOM SAMPLINGo PPS FOR SELECTING SERVICE AREAS
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OVERALL PROBABILITY
• PRODUCT OF PROBABILITIES AT EACH SAMPLING STAGE
• ACCOUNTS FOR SAMPLING DESIGN FEATURES
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DATA WEIGHTS
• INVERSE OF SELECTION PROBABILITIES
• ADJUSTMENT FOR UNIT NON-RESPONSE
• CALIBRATION – USES DATA FROM NON-
SAMPLE SOURCE FOR UNIVERSE
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VARIANCES USING PUBLIC USE FILES
• REFER TO DATA FILE DOCUMENTATION
• FOR RECENT YEARS AND BARRING RISKS,
NEEDED DESIGN VARIABLES ARE IN FILES
• RESEARCH DATA CENTER
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SUMMARY FOR ESTABLISHMENT SURVEY DESIGN
• DESIGNS USE MULTI-STAGE STRATIFIED SAMPLES
• WEIGHTS AND VARANCES REFLECT THE COMPLEX SAMPLES
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DANGERS OF NOT USING SAMPLE WEIGHTS
UNWEIGHTED ESTIMATES:• OF TOTALS WILL BE TOO SMALL
• OF RATES AND OTHER RATIOS COULD BE DISTORTED.
I.E., UNWEIGHTED SAMPLE PROPORTIONS COULD DIFFER FROM THE CORRESPONDING CENSUS PROPORTIONS
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VARIABILITY OFSURVEY ESTIMATES
• ESTIMATES BASED ON SAMPLES ARE SUBJECT TO SAMPLING VARIABILITY
• ESTIMATES OF SAMPLING VARIANCES MUST ACCOUNT FOR SAMPLE DESIGNS FOR VALIDITY
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COMPLEX SURVEY FEATURES AFFECTING VARIANCE ESTIMATION
• CLUSTERING ANALYTIC UNITS WITHIN PRIMARY SAMPLING UNITS (PSUs)
• STRATIFICATION OF PSUs
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DANGER OF USING SAMPLE SUBSETS TO ESTIMATE VARIANCES
• VARIANCE ESTIMATES BASED ONLY ON SUBSETS OF SAMPLE MAY NOT CORRECTLY REFLECT SAMPLE DESIGN
• COULD UNDERSTATE SAMPLING VARIANCE
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DANGERS OF IGNORING SAMPLE DESIGN IN VARIANCE ESTIMATION
• VARIANCE ESTIMATES PROBABLY TOO SMALL
• “DEGREES OF FREEDOM” WOULD BE TOO LARGE
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GENERAL REFERENCE FOR SURVEY ANALYSIS SOFTWARE
http://www.hcp.med.harvard.edu/statistics/survey-soft/
Provides descriptions and links to software packages that do variance estimation with complex sample data.
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