
Difficult ETT 
Not difficult ETT 
Predictive values: 
High MP score 
a)True +ve 
b)False +ve 
PPV: a/(a+b) 
Low MP score 
c)False ve 
d)True ve 
NPV: d/(c+d) 

Sensitivity: a/(a+c) 30% 
Specificity: d/(b+d) 90% 






Likelihood ratios: 


Positive LR = sensitivity / (1specificity) = 3 


Negative LR = (1sensitivity) / specificity = 0.78 
Sensitivity & specificity 
· Will pick up 30% of those with difficult ETT · Will rule out 90% of those without difficult ETT
>> unhelpful at identifying difficult intubation 
Predictive values 
· PPV and NPV ∝ prevalence · Prevalence of difficult intubation is low
>> low PPV for difficult intubation in allcomers 
Likelihood ratios 
· +LR 3: slight ↑ posttest probability of difficult intubation if high grade MP score · LR is <1: slight ↓ posttest probability of difficult intubation if low grade MP score · % Change in probability is unaffected by prevalence of difficult intubation
>> low utility in assisting prediction of difficult intubation 
Receiveroperator characteristic 
· Relationship between sensitivity, specificity, test quality · ↑AUC associated with high utility

This is my weakest topic.
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