Math 300Z: In-class group activity
Saving Lives
A tourniquet is a belt-like device used to cut off the blook supply to a damaged and severely bleeding limb. A 2014 study of 1413 US casualities in Afghanistan and Iraq concluded that “those who received tourniquets had survival rates similar to those of comparable, transfused casualties who did not receive tourniquets.” That study was careful to take into account injury severity when comparing the casualties with tourniquets to those without. (JF Kragh et al. (2014) “Transfusion for Shock in US Military War Casualties With and Without Tourniquet Use” Annals of Emergency Medicine 65(3) link)
The study authors pointed out a potential bias in the collection of data. Only those soldiers who survived up to arrival at the hospital were included.
Consider these four factors:
- Injury SEVERITY
- Tourniquet USE (at the battle location)
- ADMISSION, that is, arrival at the hospital
- Post-Admission SURVIVAL
TASK: Construct a directed acyclic graph with a node for each of these factors. Draw directed causal links between each pair of nodes that you think are likely to be connected. For each link that you draw, make sure to show the direction of causation, giviving a few words of explanation. Similarly, when there is a pair of nodes without a direct connection, explain why not.
Note: The direct paths you draw may create longer, indirect paths. For instance, \(\mathbb{A} \longrightarrow \mathbb{B} \longrightarrow \mathbb{C}\) has direct paths between \(\mathbb{A}\) and \(\mathbb{B}\) as well as between \(\mathbb{B}\) and \(\mathbb{C}\). However, there is no direct connection between \(\mathbb{A}\) and \(\mathbb{C}\).
Reference: J Pearl and D Mackenzie (2018) The Book of Why pp343-7