Transcript NATIONAL IMMUNIZATION SURVEY: SAMPLING, ESTIMATION AND PUBLIC- USE DATA FILES
NATIONAL IMMUNIZATION SURVEY: SAMPLING, ESTIMATION AND PUBLIC USE DATA FILES
__________________________________________ Michael P. Battaglia Abt Associates Inc.
Meena Khare National Center for Health Statistics July 16, 2002 1
SAMPLE DESIGN
Quarterly list-assisted random-digit-dialing sample of telephone numbers (approximately 8,500 interviews per quarter)
78 geographic strata (IAP areas)
Goal is to have an approximately equal number of children with provider vaccination history data in each geographic area
Sample management of 78 simultaneous surveys
Combine 4 adjacent quarters to obtain annualized estimates 2
RDD SCREENING PROCESS
Dial sampled telephone numbers
Identify residential numbers
Screen households (HH) for presence of children aged 19-35 months
Collect information on all age-eligible children in the HH
Stratified single-stage cluster sample design
Rare population (3.5% eligibility rate)
Average of 437 children with HH interviews per IAP area in 2000 3
INTERVIEWING PROCEDURES
Use a variety of procedures to ensure high response rates and to reduce response rate differences between the 78 geographic areas (CASRO response rate of 79% in 2000)
Conduct interview with Most Knowledgeable Person in the HH
Vaccination history from shot card or recall
Demographic and socioeconomic characteristics
Permission to contact child’s vaccination providers (obtain provider name and address) 4
ESTIMATION
Children with completed household interviews Base sampling weight – reciprocal of selection probability
Adjustment for multiple voice-use phone lines in HH
Three level unit nonresponse adjustment Eligible HH but interview not completed Known HH but eligibility not determined Unknown status (not able to determine if sample telephone number is residential, nonresidential or nonworking) 5
ESTIMATION (CONT.)
Children with completed household interviews
Combine data from 4 adjacent quarters and divide weight by 4
Poststratify to NCHS Natality File control totals within each geographic area by age category of child, race/ethnicity of mother and maternal education 6
ESTIMATION (CONT.)
Children with completed household interviews
Use technique called modified poststratification to compensate for exclusion of nontelephone children (uses NHIS immunization Supplement data on vaccination up-to-date status of nontelephone versus telephone children, and Census and CPS telephone coverage rates 7
ESTIMATION (CONT.)
In 2000, 36% of children did not have adequate provider data for use in estimation
Children with adequate provider data
Used response propensity (logistic regression) model with predictors from RDD survey
Within each geographic area divided children into (5) response propensity quintiles
Divided weights of children with adequate provider data by the weighted proportion of children with adequate provider data in their response propensity quintile 8
ESTIMATION (CONT.)
Children with adequate provider data
Used additional raking within each geographic area to ensure that weighted number of children with adequate provider data and their distribution on selected socio demographic characteristics is the same as for all children with completed HH interviews 9
PURPOSE OF NIS PUBLIC USE FILES
Provides opportunity for state and other public health researchers to analyze NIS data
The NIS Public-Use File (PUF) can be used to form national, state and IAP-area estimates of vaccination coverage rates.
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PURPOSE OF NIS PUFs (CONT.)
Analysis of age-appropriate vaccination coverage rates 11
STRUCTURE OF NIS PUBLIC USE FILES
Each PUF consists of two primary levels of data
Data for all children with completed HH interviews (34,087 in 2000)
Data for all children with adequate provider data (22,958) – excludes DISPCODE 7 children 12
STRUCTURE OF NIS PUFs (CONT.)
The phrase "children with adequate provider data" refers to children for whom sufficient vaccination history information is obtained from their providers to determine whether they are up-to-date with respect to the recommended vaccination schedule.
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STANDARD ERRORS
Information in the data file can be used to calculate standard errors of the vaccination coverage rates that reflect the complex sample design used in the NIS.
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AVAILABILITY OF NIS PUFs Year 1995 1996 1997 1998 1999 2000 Number of Children with HH Interviews 31,997 33,305 32,742 32,511 34,442 34,087 Number of Children with Adequate Provider Data 16,183 21,099 22,806 21,827 22,521 22,958 15
GEOGRAPHIC IDENTIFIERS
Each PUF includes IAP area and state identifiers
Census Region
MSA codes, county codes and ZIP codes are not included due to risk of disclosure 16
SUBGROUP ESTIMATES
Demographic and socioeconomic variables in the file can be used to obtain national vaccination coverage rates for subgroups of the population.
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SUBGROUP ESTIMATES WITHIN STATES AND IAP AREAS
Data users should, however, be aware that estimates for such subgroups at the state or IAP-area level will have larger standard errors because of the smaller sample sizes
Precision guidelines – sample size not less than 30, 95% CI half-width is not greater than 10 percentage points, half width divided by estimate is not greater than 0.50
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GENERAL VARIABLE INFORMATION
The variables in the NIS PUF fall into two major groupings:
Variables that apply to all children with completed household interviews (n=34,087 2000) and
Variables that apply only to children with adequate provider data (n=22,958 in 2000).
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NIS PUF CODE BOOK
The variables are organized into 9 sections:
ID variables, weights and flag variables
Household vaccination variables
Demographic and socioeconomic variables
Geographic identifier variables 20
NIS PUF CODE BOOK (CONT.)
Number of providers identified
Number of providers responding
Provider characteristics
Provider-reported up-to-date vaccination variables
Age in days and months at vaccination 21
COMPOSITE VARIABLES
Household composite variables Include:
Up-to-date status on individual vaccinations
Up-to-date status on selected vaccine series
Race of child and mother, household income
Child ever have chicken pox?
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COMPOSITE VARIABLES (CONT.) PROVIDER DATA COMPOSITE VARIABLES INCLUDE:
Vaccine-specific number of doses
Up-to-date status indicators for individual vaccines and vaccine series
Age at vaccination in months
Age at vaccination in days 23
COMPOSITE VARIABLES (CONT.)
Provider characteristics in the NIS PUFs have included:
facility type
types of care offered
participation in the Vaccines for Children Program 24
COMPOSITE VARIABLES (CONT.)
participation in an immunization registry
clinical specialty of person who ordered child’s vaccinations
medical home 25
ORDER OF RECORDS IN THE DATA FILE
All records in the NIS public-use data file have been sorted:
first by the unique household identification number (SEQNUMHH) and
then sorted by the unique child identification number (SEQNUMC) within each household 26
USE OF THE NIS SAMLING WEIGHTS
The NIS PUF contains two child-level weights
HY_WGT is the household interview weight variable for each child. It should be used to produce estimates for children with completed household interviews. 27
USE OF THE NIS SAMLING WEIGHTS (CONT.)
W0 is the child-level weight for the children with adequate provider data (PDAT = 1)
This weight should be used to produce estimates of vaccination coverage rates.
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BASIC SUDAAN STATEMENTS
NSEQNUMH = 1*SEQNUMHH; PROC SORT; BY ITRUEIAP NSEQNUMH; PROC CROSSTAB DATA=SUD_FILE FILETYPE=SAS DESIGN=WR; WEIGHT W0; NEST ITRUEIAP NSEQNUMH; 29
GUIDELINES FOR USING NIS PUFs
Use the documentation -- README, data user’s guide and the code book
The data file is available in ASCII format
A program is provided on the NIS web site and CD-ROMs for SAS users to convert the ASCII file to a SAS dataset
Software for analyzing complex sample designs includes SAS, SUDAAN and STATA (see Appendix F of Data User’s Guides for example of SUDAAN programs) 30
GUIDELINES FOR USING NIS PUFs (CONT.)
Use the entire file for subgroup estimates
SUBPOPN statement in SUDAAN
For estimates by geographic area (e.g., Maine, Texas) use the entire file and the SUBPOPN command in SUDAAN or just select the cases that belong the the specific geographic area (standard errors will be the same)
If only interested in vaccination coverage estimates, just select children with PDAT = 1 31
GUIDELINES FOR USING NIS PUFs (CONT.)
Missing values are imputed for key socio demographic variables except family income
For the 2000 PUF age at the birth dose of Hepatitis B is imputed if the provider indicates that a birth dose date was given – see 2000 data user’s guide
Combining multiple years of NIS data to increase sample size of children within IAP areas and states – see 2000 data user’s guide for instructions and cautions 32
VISIT THE WEB SITES
http://www.cdc.gov/nis
http://www.cdc.gov/nip/coverage 33
NIS PUF WORKSHOPS Session 36: Wednesday, 8:30-10:00 Session 41: Wednesday, 10:30-12:00 34