Using NAMCS and NHAMCS Data Linda Mc Caig

Using NAMCS and NHAMCS Data Linda Mc. Caig and David Woodwell Ambulatory Care Statistics Branch Division of Health Care Statistics National Center for Health Statistics/CDC 1

Overview l Background l Data uses l Survey methodology l Current and proposed survey items l User considerations l Methodological studies l Data dissemination l NCHS Research Data Center 2

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National probability sample surveys l National Ambulatory Medical Care Survey (NAMCS) – Patient visits to non-federal office- based physicians l National Hospital Ambulatory Medical Care Survey (NHAMCS) – Patient visits to EDs and OPDs of non -federal short-stay hospitals 4

Original NAMCS survey goals • National statistics • Professional education • Health policy formulation • Medical practice management Quality assurance • 5

NAMCS history l Survey began in 1973 l Annual data collection through 1981 (NORC) l Conducted in 1985 (NORC) l Annual began again in 1989 (Census) 6

NHAMCS history l Survey began in 1992 l Annual data collection (Census) 7

How are NAMCS and NHAMCS data used? 8

Data uses l To understand health care practice and find inequities l To track certain conditions l To establish national priorities l To serve as comparison points for states l To measure Healthy People objectives 9

Data users l Over 100 journal publications in last 2 years l Medical associations l Government agencies l Health services researchers l University and medical schools l Broadcast and print media 10

Setting government policy l ED as a “safety net” for the uninsured l Development of the Resource-Based Relative Value Scale (RBRVS) 11

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Antibiotic prescribing rates at physician office visits for children Rate per 1000 population Rate per 1000 visits 13

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Prescribing rates at physician office visits by specialty Psychiatry Ophthalmology Otolaryngology Orthopedic surgery 15

Female ambulatory care visit rates for selected diagnoses by race 16

Annual rate of illness and injury ED visits for seniors by race Illness, black 1 Illness, white 1 Injury, black 1 Injury, white NOTE: 1 p <. 01. 17

Diabetes visit rates per 10, 000 persons by setting Year Office OPD ED 1992 -93 962 84 33 1994 -95 865 117 36 1996 -97 1118 157 38 1998 -99 1289 147 49 18

NAMCS and NHAMCS Methodology 19

NAMCS Scope • Includes non-federal, office-based physicians • Excludes physicians whose main activity is teaching, research, administration, hospital-based care, or who are unclassified as to activity and those in the certain specialties 20

In-Scope NAMCS locations l Freestanding clinic/urgicenter l Federally qualified health center l Neighborhood and mental health centers l Non-federal government clinic l Family planning clinic l Health maintenance organization l Faculty practice plan l Private solo or group practice 21

Out-of-Scope NAMCS locations l Hospital ED’s and OPD’s l Ambulatory surgicenter l Institutional setting (schools, prisons) l Industrial outpatient facility l Federal Government operated clinic l Laser vision surgery 22

NAMCS Sample design l 112 NHIS PSUs l 3, 000 physicians l 25, 000 visits l 1 week reporting period 23

NHAMCS Scope l OPD was intended to be parallel to the NAMCS in the hospital setting l General medicine, surgery, pediatrics, ob/gyn, substance abuse, and “other” clinics are in-scope l Ancillary services are out of scope 24

NHAMCS Sample design l 112 NHIS PSUs l 500 hospitals l 400 EDs and 250 OPDs l 24, 000 ED visits and 30, 000 OPD visits l 4 -week reporting period 25

Gaining cooperation l Advance letters l Endorsement letters l Public relations materials l Conversion of refusal 26

Data collection procedures l Induction visit by Census field representative (FR) l FR training of office/hospital staff l Random start number l Take every number l Prospective or retrospective method 27

Items collected l Patient characteristics – age, race, sex l Visit characteristics – Reason for visit, diagnosis, medication l Provider characteristics – physician specialty, hospital ownership 28

Repeating fields l Reason for visit (3) l Cause of injury (3) l Diagnosis (3) l Ambulatory surgical procedures (2) l Medications (6) 29

Data processing l Data are coded and keyed by Analytical Sciences Inc. (ASI) l Quality control procedures l Edit checks by NCHS 30

Coding systems used l. A Reason for Visit Classification (NCHS) l ICD-9 -CM l Drug coding classification system (NCHS) l National Drug Code Directory 31

NAMCS and NHAMCS 1999 -2000 PRFs 32

Patient record form - common items l Patient’s zip code l Date of visit l Date of birth l Sex l Ethnicity 33

Patient record form - common items l Race l Source of payment l HMO status l Reason for visit 34

Patient record form – common items l Diagnosis l Diagnostic/screening services l Medications l Providers seen l Visit disposition 35

Injury items l External cause – narrative text since 1997 l Place of injury l Work related injury l Intent 36

Office and OPD PRF - unique items l Was patient referred for visit l Patient’s primary care physician l Patient seen before l Major reason for visit 37

Office and OPD PRF - unique items l Ambulatory surgical procedures l Therapeutic and preventive services l Time spent with physician (NAMCS only) 38

ED Patient record form - unique items l Arrival time l Discharge time l Immediacy l Presenting level of pain l Procedures 39

NAMCS and NHAMCS PRF revisions 2001 -02 – emphasis on the continuity of care 40

Office and OPD PRF - new items for 2001 -02 l How many visits in last 12 months l Initial or follow-up visit l Do other physicians share care l Total number of medications 41

ED PRF - new items for 2001 -02 l Discharge time l Visit related to alcohol use l Patient seen in last 72 hours l Initial or follow-up visit l Visit related to adverse drug event l Initial vital signs l Total number of medications 42

NAMCS and NHAMCS PRF revisions 2003 -04 43

ED PRF- revisions for 2003 -04 l New – oriented X 3 – is visit work related – list up to 8 medications l Recycled – mode of arrival – presenting level of pain – time seen by physician 44

2001 -02 Induction Interview revisions l NAMCS – e. g. , electronic medical records, number of managed care contracts l NHAMCS – e. g. , Pediatric Emergency Services and Equipment Supplement (HRSA) 45

2003 -04 Induction Interview revisions l NAMCS – e. g. , Physician was a member of a practice-based research network (PBRN) l NHAMCS – e. g. , Daily census of occupied and available beds 46

ED Overcrowding l Physician coverage hours l Log of ambulance diversion 47

Analysis of Facility Level Data 48

Percent of physicians who do not accept new patients by payment type 49

Distribution of hospital EDs on average waiting time 50

Overview l User considerations – Encounter vs. person data – Sampling error – Nonsampling error l Methodological studies l Data dissemination l NCHS Research Data Center 51

Encounter vs. person data l NAMCS and NHAMCS are recordbased surveys l Not population-based surveys (NHIS) l Estimates are in terms of visits and not persons l Can not calculate incidence or prevalence rates from our estimates 52

Sample weight l Sample data MUST be weighted to produce national estimates l Estimation process – Adjusts for survey and item nonresponse – Makes several ratio adjustments within and across physician specialties and hospitals 53

Sampling error l NAMCS and NHAMCS are not simple random samples l Clustering effects of visits within the physician’s practice and also physician practices within PSUs l Must use generalized variance curve or SUDAAN to calculate SEs for all estimates, percents, and rates. 54

Reliability criteria l Estimates based on at least 30 raw cases are reliable l Estimates with a relative standard error (RSE) less than 30 percent are reliable l Both conditions must be met 55

Ways to improve reliability of estimates l Combine NAMCS, ED and OPD data to produce ambulatory care visit estimates l Combine multiple years of data 56

Nonsampling error l Frame coverage l Reporting and processing errors l Biases due to survey and item nonresponse l Incomplete responses 57

Minimizing nonsampling error l Improve sample frame for better coverage l Encourage uniform reporting and eliminate ambiguities l Pretest survey items and procedures l Perform quality control procedures – consistency and edit checks l Train Census field representatives 58

NAMCS Response rates 59

NHAMCS Response rates ED OPD 60

Attempts to improve response rate l Publicity l Eliminating questions that have a high item non-response l Incentives test 61

Methodological studies • Nonresponse study • Complement study • Motivational insert • Form length • Incentive test 62

Initial results of incentives test l Still very early l Participation in some “on the fence” cases l No effect on “extreme” cases 63

Data dissemination 64

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Outside research l Journal articles – List on Ambulatory Care web site l Text books l Department level publications – Health US 66

Microdata files l Downloadable files NAMCS, 1973 -2000 l NHAMCS, 1992 -2000 l l CD-ROMs NAMCS, 1990 -2000 l NHAMCS, 1992 -2000 l l Tapes/cartridges (NTIS) NAMCS, 1973 -1997 l NHAMCS, 1992 -1997 l 67

Enhanced public-use files l SAS variable labels, value labels, and format assignments (1997 -2000) l Sample design variables – Allow use of SUDAAN and STATA – 1997 -2000 NAMCS and NHAMCS – Files prior to 2000 have been updated on web site 68

Comparison of RSEs 20 RSE 15 10 5 0 Seen by Physician assistant Cardiac monitor In-house IV fluids Masked Admitted to hosp GVC 69

Comparison of RSEs for ED visits by age 15 RSE 10 5 0 <15 15 -24 25 -44 45 -64 65 -74 75+ Patient age in years In-house Public-use 1 -stage gvc 70

Future release l NAMCS Trend file – 1980 -81, 1985, 1990 -91, 1995 -96, and 1999 -2000 l 2001 NAMCS and NHAMCS data 71

Where to get more information l Ambulatory Care information booth l Ambulatory Care website l Call Ambulatory Care Statistics Branch at (301) 458 -4600 l Academy for Health Services Research and Health Policy seminar Fall, 2002 72

http: //www. cdc. gov/nchs/about/major/ahcd 1. htm 73

NCHS Research Data Center 74

Why the Research Data Center? l Have access to information not available on public use files – Patient: zip code linked income, education, or urbanicity status – Provider: physician sex and age, board certification, teaching hospital – Geographic: state and county codes 75

Data Center-cont. l Can merge with contextual variables (e. g. , ARF, NHIS, Census, NHDS) – Health status level – HMO penetration – Physician and specialist supply – Medicaid reimbursement – Air quality – Percent in poverty 76

Data Center rules l Submit a proposal l Cannot use data to identify patients or providers or geographic location of providers l Cannot remove data files l Fee – onsite / remote / file construction 77

I need more information ! l Visit the Research Data Center booth l E-mail: rdca@cdc. gov l Website: l Call www. cdc. gov/nchs/r&d/rdc. htm (301) 458 -4277 78

Thank You l Linda Mc. Caig – NHAMCS data lmccaig@cdc. gov l David Woodwell – NAMCS data dwoodwell@cdc. gov 79

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