Understanding and Using NAMCS and NHAMCS Data:

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Understanding and Using NAMCS and NHAMCS
Data A Hands-On Workshop Part II-Using Raw Data
Files Donald Cherry
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Session Goals

• A the end of this session I would like you to
• Be able to successfully download data files and
  create a SAS dataset for analysis
• Understand some of the limitations and advantages
  of using NAMCS/NHAMCS downloadable data
• Perform simple analyses

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Using raw data files

• File structure
• Exercises using SUDAAN SAS Proc Surveymeans
• Downloading data creating a SAS dataset
• Simple frequencies with/without standard errors
• Creating a new variable-Asthma
• Visit rates-male/female
• Total number of drug mentions
• Antidepressant drug mentions
• Time spent with physician
• Trend considerations
• Other issues--multiple years/settings
• Summary

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File Structure

• Download data and layout from website
• http//www.cdc.gov/nchs/about/major/ahcd/ahcd1.ht
  m
• Flat ASCII files for each setting and year
• NAMCS 1973-2002
• NHAMCS 1992-2002

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Structure organization
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Hands-on Exercises

• Double-click My Computer\Local Disk C\DUC_04
• Double-click SAS file Exercises

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SAS version 9.1 example
proc surveyfreq datanamtest1 tables
sexager strata cstratm cluster cpsum weight
patwt2 run
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(No Transcript)
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Visit estimates
Female population800
New variable
Calculation
Phycode Sex Patwt (Patwt/Pop)100 Sexwt
1401 1 100 (100/800)100 12.5
1522 1 300 (300/800)100 37.5
1001 1 50 (50/800)100 6.25
500 1 120 (120/800)100 15
71.25
Note Rateest/popS patwt/pop1/popS patwt.
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Arrays
Phycode Patcode Med1 Med2 Med3 Med4 Med5 Med6 Total
1431 1 32905 90000 90000 90000 90000 90000 1
1431 2 95005 02995 90000 90000 90000 90000 2
1431 3 26740 90000 90000 90000 90000 90000 1
1431 4 90000 90000 90000 90000 90000 90000 0
1431 5 21228 35465 40295 90000 90000 90000 3
Total drug mentions 7
Note 90000No mention.
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Some considerations SUDAAN vs. SAS Proc
Surveymeans
SUDAAN PROC Surveymeans
design variablescstratm, cpsum (1-stage design) design variablescstratm, cpsum (1-stage design)
nestcstratm, cpsum strata cstratm cluster cpsum
Sort by design variables Sort not needed
Weight data Patwt2 Weight data Patwt2
Subgroupidentify categorical variables Classidentify categorical variables
Tablesanalysis variables Varanalysis variables
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Trend considerations

• Variables routinely rotate on and off survey
• Be careful about trending diagnosis prior to 1979
  because of ICDA (based on ICD-8)
• Even after 1980- be careful about changes in
• ICD-9-CM
• Number of medications varies over years
• 1980-81 8 medications
• 1985, 1989-94 5 medications
• 1995-2002 6 medications
• 20038 medications
• Diagnostic therapeutic checkboxes vary
• Use spreadsheet for significance of trends

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Combining multiple years

• 2 year combinations are best for subpopulation
  analysis
• 3-4 year combinations for disease specific
  analysis
• Keep adding years until you have at least 30 raw
  cases in important cells
• RSE improves incrementally with the number of
  years combined

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RSE improves incrementally with the number of
years combined

• RSE SE/x
• RSE for percent of visits by persons less than 21
  years of age with diabetes
• 1999 RSE .08/.18 .44 (44)
• 1998 1999 RSE .06/.18 .33 (33)
• 1998, 1999, 2000 RSE .05/.21 .24 (24)

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Combining multiple settings

• NAMCS, ED, and OPD can be combined in one or
  multiple years
• NAMCS OPD variables virtually identical, many
  ED variables are same
• OPD and NAMCS should be combined to get estimates
  of ambulatory physician care especially for
  African-American, Medicaid or adolescent
  subpopulations
• Only NAMCS has physician specialty

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Design VariablesSurvey Years
2002
2001
1-Stage design variables 3- 4-Stage design
variables
3- 4-Stage design variables
2003
1-Stage design variables only
Plan to re-release years with 1-stage design
variables.
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Code to create design variables survey years
2001 earlier
CPSUMPSUM CSTRATM STRATM IF CPSUM IN(1, 2,
3, 4) THEN DO CPSUM PROVIDER 100000 CSTRATM
(STRATM100000) (1000(MOD(YEAR,100)))
(SUBFILE100) PROSTRAT END ELSE CSTRATM
(STRATM100000)
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If nothing else, rememberThe Public Use Data
File Documentation is YOUR FRIEND!

• Each booklet includes
• A description of the survey
• Record format
• Marginal data (summaries)
• Various definitions
• Reason for Visit classification codes
• Medication generic names
• Therapeutic classes

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Where to get more information?

• www.cdc.gov/nchs/about/major/ahcd1.htm
• Call Ambulatory Care Statistics Branch at
  301-458-4600