2020B14 Mallampatti score is a diagnostic test for difficult intubation with a sensitivity of 30% and a specificity of 90%. Describe how this information and other statistics related to this test can be used for predicting difficult intubation. How does the prevalence of difficult intubation affect the performance of this test?

	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 / (1-specificity) = 3
	Negative LR = (1-sensitivity) / 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 all-comers
Likelihood ratios	· +LR 3: slight ↑ post-test probability of difficult intubation if high grade MP score · -LR is <1: slight ↓ post-test 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
Receiver-operator characteristic	· Relationship between sensitivity, specificity, test quality · ↑AUC associated with high utility

This is my weakest topic.

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