Multiple cause of injury data: Selecting a main injury

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Multiple cause of injury dataSelecting a main
injury

• Margaret Warner, Ph.D.
• Injury ICE meeting
• Mexico 2005

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Overview

• International differences in multiple cause data
• Methods to analyze multiple cause data
• Selecting a main injury from MCOD
• Looking at commonly co-occurring injuries

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Multiple cause data for injury deathsUnited
States
Up to 20 conditions mentioned on death
certificate including

• External cause of injury
• Underlying cause
• U,V,W,X,Y codes
• Intent and cause
• Injury diagnoses
• S and T codes
• Body region and nature
• Other diagnoses
• A,B,CR codes

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Difference in multiple cause data

• Do not code multiple cause of death
• Canada
• Code all causes, do not select main injury
• United States
• Code all causes and select a main injury
• England Wales
• Code only a main injury
• ???

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Multiple injuries listed per death
Percent of deaths by number of injuries coded
Average number of injury codes
1
2
3 or more

• USA 1.53 65.1 22.2 12.7
• (1999)
• Sweeden 1.48 61.7 27.9 10.4
• (1987-96)
• Scotland 1.26 74.7 21.0 3.0
• (1996-98)
• England Wales 1.34 74.5 19.3 6.2

(1996-98)
1.74 if duplicate codes included
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Multiple injury deaths

• Many methods to analyze. For example
• Total mentions of injury diagnoses
• Any mention (i.e. at least one mention)
• Weighted total mention
• weight 1/total number of injuries per death
• Main injury or first listed injury

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Number of Mentions Total, Any Weighted
total by body region US, 2002
Body region
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Why select main injury?

• Data issues
• May differ by certifier
• Artifacts of coding rules
• ICD international and some countries only collect
  the main injury

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If select main injury, is information lost?

• Is one injury more important than the other???
• Rules can be established about priority, but what
  conclusions will be drawn from data
• Are there combinations of injuries which are more
  deadly?

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ICD and selecting a main injury

• ICD-10 Vol. II, Section 4.2.10
• ICD-9 Precedence list most severe
• ICD-10 Selects the initiating condition
  (similar to external cause)
• Asked for input from the Mortality reference
  group (MRG)
• MRG (1) decides on applications and
  interpretation of the ICD to mortality and (2)
  recommends updates to ICD

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Selecting a main injury Recommendations from MRG

1. Eliminate trivial injuries and superficial
   injuries from consideration
2. If obvious causal sequence, select injury which
   led to death
3. Select from among remaining injuries using
   severity ranking (e.g. Precedence list)
4. Select first mentioned if several at same level
   of severity

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Analyze data by common pairs of injuries

• To determine if certain combinations commonly
  occur together (e.g. head and thorax injuries)
• If yes,
• Computer algorithms could be adapted to choose
  for these deaths
• Should a single code by used to identify
  combination?

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Common pairs, US, 2001

• 157,078 deaths with external underlying cause
• 1 injury listed 65 of deaths
• 2 injuries 22
• 3 injuries 8
• 4 -15 injuries 4
• Examined unique pairs
• Two nature of injury codes were treated as a
  unique pair regardless of the order in data

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Common pairs

• TRUE !!!!
• Certain injury pairs account for high proportion
  of deaths with two or more injuries listed

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Common pairs, results

• Most frequent pair occurs 3,327 times
• S06.9 (Intracranial injury, unspecified) and
  S09.9 (Unspecified injury of the head)
• Second most frequent occurs 2,671 times
• S09.9 (Open wound of head, part unspecified) and
  S29.9 (Unspecified injury of the thorax)

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Expert review of 139 pairs

• Member of MRG and expert ICD coder
• Selected main injury for 83 (116 out 139)
• Main injury selected for 54 of deaths with 2
  injuries listed

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Unspecifieds

• Many injuries are unspecified either by body
  region or by nature
• Totally non-specific ICD codes
• T14.8 Other injuries of unspecified body
  region
• T14.9 Injury, unspecified

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For 2 injuries listed
Pair with Percent distribution
T14.8 (Other injury unspecified ) 2.6
T14.9 (Injury, unspecified) 8.4
Superficial injuries 1.1
Selected by expert review (116) 54.0
Total Main injury selected for 64.0
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Conclusion

• Multiple cause data vary by country
• Number of injuries reported and coded
• Range 0, 1, 20
• Some select main injury, others keep all
• Many methods to analyze (total, weighted total)
• Selecting main injury (ICD rules might be
  modified)