# Presentation: 191215

## Multiple cause of injury data:Selecting a main injury 

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

**Notes:**
Good Morning.  My name is Margaret Warner.  I have been leading the group working on the multiple cause of injury data.

## 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

**Notes:**
Today I am going to only be able to touch on some of the research ICE members have done in this area.
First I am going to briefly touch on international differences in multiple cause data including how the data are recorded 
 Since most countries record more than one injury in the MC data. I am going to touch on methods to analyze the multiple causes
 I am going to show you the ICD-10 injury mortality diagnosis matrix developed by members of ICE which is used for presenting the MC data
 Next I will talk about the work we have been doing on methods to select a main injury
 Show results of how some injuries occur at the same time...

## Multiple cause data for injury deathsUnited States

- 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,C...R codes**

**Up to 20 conditions mentioned on death certificate including ...**

**Notes:**
Just to familiarize you with the “language” I will use.  Using the setup of the US data as I guide...
In the US we have up to 20 conditions mentioned on the death certificate...
All the conditions are coded using ICD-10.    
I use the following terms – 
the external cause is the UVWXy
The injury diagnoses is the S and T codes
And then everything else...

## 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
**???**

**Notes:**
Multiple cause data differs by country.
In Canada, for instance, they do not collect mc data on injuries
In the US, we collect and code all causes but we do not select a main injury
In England and Wales, they collect, code and select a main injury
I know there are countries that only code one main injury (in other words, select one and then code it)

## 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

-    (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

**Multiple injuries listed per death**

*Average*
*number of injury codes*

*1*

*Percent of deaths by number of injuries coded*

*2*

*3 or more*

- (1996-98)

- * 1.74 if duplicate codes included

**Notes:**
Here is a table put together by some ICE collegues comparing the multiple cause data between countries.  They found that the number of injuries coded varies by country.  The US had the most injuries coded with an avearage of about 1.7 injuries per death and the Scotland had the fewest with about 1.3 per death.   Some of these differences may be true differences between countries but we suspect a lot is due to reporting and coding differences.

## 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

**Notes:**
Since many deaths may have more than one injury listed, the method of summarizing the data needs to be considered carefully.
The most straightforward is to count up each diagnosis code and report the total number.  For instance, in the US in 2002 there were 161 thousand deaths due to an external cause.  Each death had about 1.5 injury diagnoses listed so there were a total of 246 thousand injuries recorded.

Another method is to state the number of times an injury was mentioned.  For instance, there were 58.5 thousand deaths with any mention of a head injury.

The weighted total mention involves weighting each injury in a death by the inverse of the number of injuries in that death.  So if a person had a head and Chest injury – the head injury would count 1⁄2 and the chest injury would count as 1⁄2.   This method is convenient because the total number of injuries adds up to the number of deaths.  

Finally, we have been working at trying to find a method to select a main injury.  For looking at international data, I think this may make the most sense since it appears that there are differences in methods of recording between countries

## Number of Mentions: ‘Total’, ‘Any’ & ‘Weighted total’ by body region US, 2002

- Body region

**Notes:**
Here are the 2002 US multiple cause data using the first three methods and the matrix.

## Why select main injury?

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

**Notes:**
So now I am going to talk about selecting a main injury...  Having looked at the US data, I think it may be important to select a main injury since some of the reason that some deaths have one injury and some deaths have many injuries may not be due to the death...  I suspect this is true internationally.  Some differences are likely due to the certifier and others may be artificacts of coding... For instance, in the US, coders are supposed to code to the finest level of detail available.   In other words code each injury and avoid using codes describing multiple injuries

## 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?

## 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

**Notes:**
So now I am going to talk about selecting a main injury...  Having looked at the US data, I think it may be important to select a main injury since some of the reason that some deaths have one injury and some deaths have many injuries may not be due to the death...  I suspect this is true internationally.

Here are some of the downsides to selecting and some of the things the MCOD group have been discussing.

## Selecting a main injury: Recommendations from MRG

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

## 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?

## 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**

## Common pairs

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

## 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)

## 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

## 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

## 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 % |

## 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)