# Presentation: 717676

## Injury and Poisoning Estimates from the National Health Interview Survey-Why They Differ from Other Estimates

**Manon Boudreault MPH,  Margaret Warner PhD, and  Lois Fingerhut, MA**

**National Center for Health Statistics**

**U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES**

**Centers for Disease Control and Prevention**

**Office of Analysis and Epidemiology**

**2005 National Injury and Prevention and Control Conference, Denver, CO**

## Overview

**National Health Interview Survey**
- 	-Questionnaire History
- 		-Current data
**Other Injury Data from NCHS**
- 		-Comparison of data sources
**Linking NHIS files and public-use data files**

## 
All medically-attended  injuries occurring to any family member during the 3 month period prior to the interview are asked about from an adult family member.

Uses a multistage sample designed to represent the U.S. civilian non-institutionalized population

Collected throughout the year, nearly 40,000 households are visited (info on over 90,000 persons)

**All **_**medically-attended**__** **_** ****injuries occurring to any family member during the 3 month period prior to the interview are asked about from an adult family member.**
**Uses a multistage sample designed to represent the U.S. **_**civilian non-institutionalized**_** population**
**Collected throughout the year, nearly 40,000 households are visited ****(**_**info on over 90,000 persons**_**)**

_**NHIS**_

**Notes:**
Census Bureau field representatives conduct interview (using CAPI-Computer Assisted Personal Interviewing)

## NHIS Strengths

**More detailed information**:
**circumstances, cause, and location of episode**
-               (64% of the adult episodes are self-reported)
**Nearly complete external cause codes**
**Largest range of data available in one system**
**Linkable with other national data sets**

## Data prior to the redesigned 1997 NHIS

**Placement, phrasing and number of questions**
**Recall period**
**Severity threshold**

***Prior years are not directly comparable due to:***

***25%******   injuries due to these and other changes***
***	******	******	******	******(1995 to 1997)***

**Notes:**
In 1997, the injury and poisoning section of the NHIS was redesigned to address criticism about the lack of detail collected on the circumstances of the event in question and the limitations in analyses related to sample size.  Previous studies have suggested that as the recall reference period increases, minor injuries are less frequently reported.  Thus, the severity threshold for inclusion of an injury episode in the redesigned NHIS was raised to include only medically attended events (and would presumably be less likely to be forgotten).  Prior to the redesign, injuries resulting in at least one-half day of restricted activity were also included.
1958-1996
	Screener questions throughout
	Recall: 2 weeks
	Severity threshold: medical advice and/or 1⁄2 day restricted activity
	Limitations:
		-lack of details for cause/circumstances
		-no specific questions on poisoning

Recall period was lengthened to increase the sample size.  Other changes include stricter injury definition. 
The 1997 estimate when limited to medically attended injuries and excluding the adverse effects was 25% lower than the 1995 estimate.

## Analysis of Recall Bias

- Questionnaire recall period ...**past 2 weeks****?** (before 1997) to... **past 3 months****?** (current)
**More severe injuries** (fractures and sprains/strains) **showed similar numbers** whether recall was 2 weeks or 3 months.
- Further analyses showed drop in reporting minor injuries after 5 weeks.

**“****Recall Bias”****	**

***Fewer minor injuries reported***

**Notes:**
This suggests that the recall of less severe injuries may be playing a role in the decrease in estimated number of injuries.  However, the estimates were made more stable with the 3-month recall because of the greater number of observations on which the estimates are based.

Work is currently ongoing to make a 5-week analysis variable available in a separate public-use data file.

## Annual estimates (NHIS) of injury and poisoning episodes

**Episodes in millions**

**Year**

**Detailed questionnaire history:**
** **_[http://www.cdc.gov/nchs/about/otheract/injury/presentations.htm](http://www.cdc.gov/nchs/about/otheract/injury/presentations.htm)__ _

**Notes:**
After analyzing the data from the 1997 survey, a number of issues were noted. 	

Data issues: 1997-1999 	

Some questions not common to both injuries and poisonings
 Injuries recorded as poisonings and poisonings recorded as injuries
 High proportion in Other 
  No question on treatment location 	

In order to get the changes into the 2000 questionnaire - changes were made without testing.

Changes: 1997-99 to 2000 Survey
 Combined injury and poisoning 	questions
Added a question about medical advice or treatment
Revised categories for several questions

Screener questions: One combined question...”injury or poisoning” 
Other questionnaire changes:
	-added question about advice or treatment location (e.g., phone, ED, hospital, etc.)
	-shortened section introduction (for respondent), combined I/P sections for common set of instructions
	-interviewer help screens expanded
Limitations:
-single set of screener questions
-inadvertent change to wording of key question

## “Packed” question

**2000-03: **DURING THE PAST THREE MONTHS, that is since {91 days before today date}, {were/was} {you/anyone in the family} **injured** or **poisoned** seriously enough that {you/they} got **medical advice or treatment**?

**Three questions in one:**
**Were you injured?**
**Were you poisoned?**
**Did you seek medical advice?**

**Notes:**
Both discussions with the interviewers and the cognitive testing suggested that our screen question was really three questions packed into one – and that perhaps people were not hearing the injury part of the question.  So in  2004  the question was  “unpacked”

## “Unpacked” question- NHIS  2004

- During the past three months, that is since {January 2}, did you have an** ****injury where any part of your body was hurt, for example, with a broken bone, sprain, burn, wound, bruise, or animal or insect bite?**
- During the past three months, that is since {January 2}, were you **poisoned by swallowing or breathing in a harmful substance such as bleach, carbon monoxide, or too many pills or drugs?**
**Did you ****talk to or see a medical professional**** ****about this {injury/poisoning}?**

**Notes:**
For the 2004 survey, changes included unpacking the question and adding examples of what constitutes an injury and a poison

Collection of Injury and Poisoning Data in the NHIS, 2004
Screener questions (2): One each for injury and for poisoning
Other question changes:
	-Rotating preset list of examples read to respondent (rotated order, and type of examples), more detailed examples of an “injury” and of a “poisoning”
Limitation:
	-Analysis of trends

## Annual estimates (NHIS) of injury and poisoning episodes

**Episodes in millions**

**Year**

- *

- New
- questions

*****

- *Preliminary data, anticipated substantial increase based on revised questions.

**Notes:**
The preliminary 2004 estimate collected using the revised survey (new “unpacked” questions with examples) shows a substantial increase in the number of injuries and poisonings reported from 2003." 

## Comparison of Other NCHS Data Sources with the NHIS

## Important Factors Related to NHIS Estimates  

- Recall period effects reporting of minor injuries
- Proxy reporting for all children and 36% of adult i/p episodes
- Relatively few intentional injuries reported
- Total treatment may not be reported
- Institutionalized population not captured, e.g., nursing homes
- Acute injury episodes rather than chronic injury

## Annual rate of injury-related ED visits for seniors by patient residence: 2001-2002

| Age in years | Institution | Community |
| --- | --- | --- |
|  | Number of visits per 100 persons |  |
| 65-79 | 41 | 8 |
| 80+ | 37 | 14 |

- From the NCHS **2004 Data Users Conference Presentation **
**Overview of the NAMCS and NHAMCS** by Linda McCaig and David Woodwell
- http://www.cdc.gov/nchs/ppt/ahcd/Sess_10_Intro_NAMCS_WOODWELL_&_McCAIG.ppt

- Institution is defined as a nursing home or other institution, such as a prison,
- mental hospital,  group home for the mentally or physically disabled.
- Source: NCHS, NHAMCS-ED

**Notes:**
Since the NHIS excludes the institutionalized people, this is one group of individuals not captured in the NHIS who have a higher risk of injury.
2002 CMS (Centers for Medicare and Medicaid Services) Medicare enrollees ages 65 and over in long-term care facilities (nursing homes) 4.8 percent, 18.6 percent of those 85 and over.  In Older Americans 2004, Key Indicators of Well-Being, Table 36A, found online at:  www.agingstats.gov

## Injury poisoning episodes (all), pain/swelling* due to injury (adults), and some disability due to injury (adults): 1997-2003

- In millions

**Injury/poisoning episodes-all ages-(I/p file)**

**Adults- *pain/ache/stiffness/swelling due to injury-(sample adult file)**

**Adults w/some disability due to injury-(sample adult file)**

**1997**

**1998**

**1999**

**2000**

**2001**

**2002**

**2003**

**i/p episodes**

**disability**

**pain**

**Notes:**
This slide shows injury information obtained from different sections of the NHIS.  From the family section (where a knowledgeable adult answers for the family members-all adults are invited to participate if available) are the injury episodes in the teal-colored bars and from the adult sample section of the survey other information related to injury can be found (pain and disability due to injury).  The light blue bars show the number of adults who have had pain/aching/stiffness/swelling/redness due to an injury in the past year and the navy bars show the number of adults who have some functional activity limitation (such as bending, stooping, walking, etc.) and report that this limitation is the result of an injury. These data are not mutually exclusive although determining the precise overlap cannot be determined for most and would be based on probability as such. Some difficulty to not being able to bend, stoop, or kneel was the most common disability identified.  Knees, shoulders and ankles in ranking order were the joints most commonly mentioned affected by an injury and for all, 60% reported that these symptoms were present for most days for at least a month.  For the disability due to injury, questions are asked about how long they have had the injury condition.  The next slide shows that for most who report some limitation due to injury, they’ve had the injury condition for more than a year.

## Some disability due to injury: 1997-2003 

- Number of adults in millions

- *Selected from a printed condition list as “fracture/bone/joint injury” and/ or “other injury”
-   (sample adult section/file)

**Injury condition duration:**

**Notes:**
These data are from a different section of the NHIS, where a sample adult is asked specific health questions and proxy reporting generally is not allowed. From this slide, the impact of injuries for many is long-term. 

## NCHS Injury Data SourcesMedical/Administrative RecordsHousehold Interview

## Injury-related treatment:  NHIS/other NCHS surveys  

| Household Interview |  |  |
| --- | --- | --- |
| NHIS episodes (2002) | 23.7 million episodes | NHIS Treatment reported (2002)  |
|  |  |  |
| Medical Records-2002 Estimates |  | NHIS |
| NHAMCS
ED visits | 33.0 million | 13.1 million |
| NHAMCS
OPD visits | 10.2 million | 3.0 million |
| NAMCS
Dr. visits | 99.2 million | 8.2 million |
| NHDS-discharges | 1.8 million | 1.0 million |

**Injury-related treatment:  NHIS/other NCHS surveys  **

**Notes:**
For data year 2000 and onward, a question was added on the NHIS that asked about treatment location.  Not shown on this slide are an additional 1.2 million calls to the Dr.’s office and 198,000 calls to the poison control center reported.  As you can see, the treatment reported in the NHIS is much lower than what is shown for other NCHS surveys.  These other data based on medical records, capture multiple visits for the same injury, chronic conditions related to injury, and a more accurate account of all health services utilization related to injury.  Of note, is the large difference between actual physician-based office visits due to injury and reported dr visits in the NHIS.  A portion of these are probably more minor injuries that may not have been remembered and reported in the NHIS.  The estimates between the more severe injuries (hospitalizations) and the NHIS were the most similar which is consistent with previous research that found more severe injuries are better remembered than minor injuries.

## Treatment reported in the NHIS

- All treatment received most likely not reported—only 16 percent of those hospitalized with a fracture also reported a visit to a doctor.
- Compared with other NCHS treatment administrative databases, differences in frequency were greatest for physician-based office visits.
- Fracture ED visits and reported fracture NHIS ED visits were the most similar (1.4 times the NHAMCS-ED).

## Medical Records-Based Data

- More accurate accounting of total treatment / healthcare utilization
- Treatment, procedures, and prescribed drug information available

- Collection limited to what’s entered on form/medical chart
- Automated collection systems may differ (NHDS)
- Injury mechanism/cause often unspecified

**Strengths**

**Limitations**

## Percent with unspecified cause of injury: 2002  

| 
NHIS episodes | 
2.6% |
| --- | --- |
| NHAMCS
ED visits | 
26% |
| NHAMCS
OPD visits | 
49% |
| NAMCS
Dr. visits | 
45% |
| NHDS-discharges | 36% |

**Percent with unspecified cause of injury: 2002  **

**Notes:**
Here is the percent with unspecified cause of injury by data source.  For the NHIS episodes nearly all are E-coded.  Narrative text is reviewed and coded by external contractors to ICD-9-CM codes.  Frequently, for the data based on medical records, the E-code, is missing. 

## NHIS Public-Use Files and Linking 

## NHIS-Public Use Data Files

- For estimated annual injury and poisoning episodes:
- 			-Person file
- 			-Injury and poisoning episode file
- 			-Injury verbatim file
- Using SAS, STATA, SPSS

**Notes:**
For the injury and poisoning episodes and injury conditions presented today, the documentation and files are available on the web site listed at the end of this presentation. 

For the injury and poisoning episodes several files need to be merged before estimates can be calculated.  The person file, and the injury and poisoning episode file (could include injury verbatim file).  These are merged using three variables HX PX and FX.  For the individual files, the NHIS website has SAS, STATA, and SPSS input statements that you can download directly from the web.  We can email you a SAS program that shows how to merge these files.  For data years 1997-1999 the poisoning episodes are in a separate file. 

## NHIS Links Expand Scope of Available Injury Data

**More within NHIS**
- -Sample adult
- -Sample child
**External links to NHIS**
- -Medical Expenditure Panel Survey (MEPS)/NHIS linkage
- -National Death Index (NDI)/NHIS linkage

**Notes:**
In other parts of the NHIS survey, the sample adult and the sample child files (where a knowledgeable adult answers for the child) can supplement and expand the wealth of information available for the i/p episodes.  In 2003, from the sample adult file,  detailed health and behavior information (such as alcohol use, BMI, other diseases) were linked with over half of the adult injury and poisoning episode records.

As a separate data effort, NCHS has worked with the Agency for Healthcare Research Quality so that the NHIS files can be linked with the Medical Expenditure Panel Survey (MEPS) data. The National Health Interview Survey (NHIS) and the Agency for Healthcare Research and Quality's Medical Expenditure Panel Survey (MEPS) each release annual files. Beginning with the 1995 NHIS and the 1996 MEPS, these files can be linked. The NHIS/MEPS linkage files allow users to link persons in the MEPS public use files to the records of the same persons in the previous NHIS public use files.

NCHS has conducted a linkage of the National Health Interview Survey (NHIS) with the National Death Index (NDI).  Linkage of the NHIS survey participants with the NDI provides the opportunity to conduct studies designed to investigate the association of a variety of health factors with mortality, using the richness of the NHIS core and supplement questionnaires. The National Health Interview Survey (NHIS) linked mortality files contain information based upon the results from a probabilistic match between NHIS and the National Death Index (NDI) records. The National Death Index (NDI) is a central computerized index of death record information on file in the State vital statistics offices.  Working with these State offices, NCHS established the NDI as a resource to aid epidemiologists and other health and medical investigators with their mortality ascertainment activities. 

## NHIS Injury/Poisoning Episodes linked with NHIS Sample Adult File 

**Sample Adult Questionnaire**
- 	-Cigarette smoking
- 	- physical activity
- 	-alcohol consumption
- 	- height and weight
- 	-gender specific questions
- 	-specific and chronic conditions
- 	-respiratory ailments
- 	-sensory impairment
- 	-mental health
- 	-health care access and utilization

**Notes:**
From each family, with a household member over the age of 17, a sample adult is randomly selected by the computer, and asked more detailed health related questions.

##  NHIS Links with Other National Data Sets

**MEPS/NHIS Link**
- 		-1995 NHIS/1996 MEPS to
- 		2002 MEPS/2001 and 2000 NHIS links
- 		-***Health services used, cost of services, and how paid.***
**NDI/NHIS Link**
- 		-2004 linked file includes NHIS survey years
- 		1986-2000 with mortality follow-up through 2002
***-Age at NHIS interview, ***
***-underlying and multiple cause of death***
***-Other variables by special request (e.g., occupation)***
***http://www.cdc.gov/nchs/about/major/nhis/nhismep.htm***
***http://www.cdc.gov/nchs/r&d/nchs_datalinkage/nhis_data_linkage_activities.htm***

**Notes:**
Here are two other external linked data sets that provide additional information to the data collected in the NHIS.  As shown, here are the data years available for the merged data and a brief description of the type of information available on these other data sources.

Due to confidentiality requirements, the 2004 NHIS Linked Mortality files only are available through the NCHS Research Data Center (RDC). All interested researchers must submit a research proposal to the RDC to use the NHIS linked mortality data.  The RDC offers both on-site and remote user access. Approved researchers will be able to analyze data from the NHIS standard mortality file which contains information on NHIS participant eligibility status, vital status, date of death, age at death, and underlying and contributing causes of death.  Additional death certificate data are available by  special request. Requests for access to special request variables should be clearly documented in the researcher’s RDC proposal.

## National Health Interview Survey

- Much more detailed info on cause /circumstances
- Provides national estimates  collected from persons not records
- Largest range of data available in one system
- Responses to specific prevention questions
- Linking to other major data systems

- Proxy reporting
- Recall bias
- Intentional injuries masked or underreported
- Missing institutionalized population (e.g., nursing homes)

**Strengths**

**Limitations**

## Questions or additional informationnchsinjury@cdc.gov mboudreault@cdc.govNHIS:  www.cdc.gov/nchs/about/major/nhis/quest_data_related_doc.htmInjury Data and Resources Website!http://www.cdc.gov/nchs/injury.htm

**Notes:**
Please let us know if you need additional information or would like the merging program.  You can visit our Injury data and resources website for more injury-related information.  Thank you.