Measuring Injury Using the National Health Interview Survey
Margaret Warner, PhD Lois A. Fingerhut, MA Pat Barnes, MA
National Center for Health Statistics
CDC
CENTERS FOR DISEASE CONTROL AND PREVENTION
Location of injury and poisoning data
• Injury Episode file • Injury Verbatim file • Poison Episode file • Person file
Injury episode file
For each person:
• Up to 4 injury episodes
For each episode:
• Up to 4 ICD-9-CM diagnosis
codes
• Up to 3 ICD-9-CM external
cause codes
Available data in the Injury Episode file
• External cause (ICD-9-CM)
• Injury diagnoses (ICD-9-CM) • Place of occurrence • Activity • Resulting limitations • Detail on certain causes (e.g.
mv crashes, falls)
Injury episode file
ICD-9-CM diagnosis codes and E-codes are based on information supplied by respondents, not medically trained personnel.
Poisoning episode file
• Contains no ICD-9-CM codes or
E-codes
• Contains 47 episodes coded as
“Allergic/adverse reaction to medical or other substance” or “Something else – not poisoning”
Available data in the Poisoning Episode file
• Cause of poisoning • Call to poison control center
Available data in both injury and poisoning files
• Date of episode
• Hospitalization • Days out of school • Days out of work • Time elapsed between episode
and interview
Injury section–Person file
• Contains summary information
about injury and poisoning episodes
• Annual estimates can only be
made on variables INJCT and POICT
How do I put the data together?
Injury and poisoning episode, and injury verbatim files
• Contain only injury or
poisoning information and unique identifiers
• Must be linked to the person
file to obtain sociodemographic variables, design variables, etc.
Episode and person based files
Episode based: A person will appear in these files as many times as he/she has a unique episodes Person based: A person will appear in this file only once
Concatenating injury and poisoning episode files
Injury
+
Poisoning
Injury Poisoning
= Missing data, questions not found in both files
Merging injury/poisoning episode file and person file
Injury
Poisoning
+
Person
= Missing data, questions not found in both files
Merged injury/poisoning episode file and person file
Injury
Poisoning
Person
= Missing data, questions not found in both files
Episodes and Conditions
• Episode = Event that caused the
condition (e.g. fall down stairs)
• Conditions = physical harm
resulting from the injury episode (e.g. broken leg, bruised arm)
Creating condition files Injury
Injury Episode with ICD9_1 ICD9_2 ICD9_3 ICD9_4
ICD9_1 ICD9_2
ICD9_3 ICD9_4
Creating condition files Poisoning
Poisoning episode
=
Poisoning condition
Concatenating injury and poisoning condition files
Injury conditions
+
Poisoning
Injury conditions
Poisoning conditions
= Missing data, questions not found in both files
What Can I Do With the Data?
Handout
• Using SAS to manipulate the
injury and poisoning data
• Example SAS programs for
concatenating and merging the files
Analyzing the injury and poisoning data
• Estimates of frequency • Percent distributions • Rates • Standard errors
Calculating annual estimates
• Annual est = (variable)(4)(WTFA) • Annual estimates of episodes
and conditions can be calculated.
• Annual estimates of the number
of persons injured cannot be calculated due to the 3 month reference period.
Standard Errors (SE)
• SE of the injury/poisoning rate
for males and females
• SE of the injury/poisoning rate
for specified racial groups
Estimates of frequency
Examples
• Number of episodes resulting
from specific causes
• Number of injury/poisoning
episodes by sex
• Number of injury/poisoning
episodes by mechanism
Results
F re q (m illio n s) 1997
E p iso d e s C o n d itio n s
3 4 .4 4 0 .9
Rates
Examples
• Annual injury/poisoning rates
for males and females
• Annual injury/poisoning rates
by mechanism
• Annual rate of falls for females
over 65 years of age
Injury and poisoning episode rates
Age in years
Under 12 12-21 22-44 45-64 65+ 65-79 80+ 0 50 100 150 200 250 300 Male Female
95% CI
Episodes per 1,000 population
Age adjusted injury episode rates by mechanism of injury
Fall Struck Trans Overexertion Cut Poisoning
Both Sexes Male Female
0
10
20
30
40
50
60
Episodes per 1,000 persons
Age adjusted condition rates by type of injury, 1997
Sprains/Strains Open Wounds Fractures Contusions Internal Organs 0 5 10 15 20 25 30 35 40 45 50
Both Sexes Male Female
Percentages
Examples
• Percent of episodes resulting
from specific causes
• Percent of poisoning
episodes in which a poison control center was called
• Percent of injury episodes that
occurred in the home
Percent of injury episodes by place of injury, 1997
Home (inside) Home (outside) Street/highway Sport facility Industrial/construction School Trade/service Park/recreation area Other public building
Male Female
0
5
10 15 20 25 30 Percent of episodes
35
40
Persons could indicate up to two places per episode.
Work-related injuries
• Injury episode file:
Activity at the time of injury= Working at a paid job
• Sample person file:
Occupation and industry
Percent of injury episodes by activity, 1997
Leisure Working paid job Sports Working (house/yard) Driving Attending school Unpaid work
Male Female
0
5
10 15 20 25 Percent of episodes
30
Persons could indicate up to two places per episode.
Injury verbatim file
•
Responses recorded by the interviewer:
• How the injury occurred • Body part injured • Nature of injury
•
Text file linkable to other files
Available data in injury verbatim
• How the injury occurred
(up to 336 characters)
• Up to 4 body parts injured
(up to 34 characters each)
• Up to 4 nature of injuries
(up to 44 characters each)
Injury verbatim file
• Edited only for confidentiality • Grammatical and/or spelling
errors were not corrected
Uses of injury verbatim
• NCHS used to code ICD-9-CM
diagnoses and external causes
• Code according to other
classification schemes (e.g. BLS, ICECI, etc)
• Text search for words of interest • In-depth analysis of ICD-9-CM
categories
Check sample size
Analysts should be cautioned against making estimates based on small numbers of observations.
Verbatim text Example
Cause of injury: “While , . fell on thumb.”
Part of body: “Right thumb”
Type of injury:
“Broken”
Examples of verbatim Machinery related injuries (E919)
• “He was at home working on his
table saw and accidentally ran his left thumb through the machine lengthwise.” (table saw, n=8)
•
“Forklift extension came loose dropping on right foot at work” (forklift, n=3)
Contact for questions related to injury data or injury classification issues:
MWarner@cdc.gov