Table 1. Examples of calculating clinical validity and population impact.

Example	Empirical data		Hypothetical data
	Abacavir		Simvastatin
Study	Mallal et al.9	Mallal et al.9	SEARCH collaborative group10	Voora et al.11
Variant	HLA-B*5701	HLA-B*5701	SLCO1B1 c.521T>C (*5)	SLCO1B1 c.521T>C (*5)
Risk genotype freq	6.7%	6.6%	25%	28%
Adverse event	Clinically diagnosed abacavir hypersensitivity	Immunologically confirmed abacavir hypersensitivity	Severe myopathy	Any side effect
Adverse event freq	8.5%	3.1%	0.8%	23%
ORa	30	1176b	8.5	2.8
Sensitivity	48%	100%	73%	45%
Specificity	97%	96%	76%	77%
PPV	60%	47%	2%	37%
NPV	95%	100%	99.7%	83%
PAF	44%	100%	64%	24%
NNT	2	3	49	6
NNG	27	33	195	19

Abbreviations: NNG, number needed to genotype; NNT, number needed to treat; NPV, negative predictive value; PAF, population attributable fraction; PPV, positive predictive value. Severe myopathy: muscle symptoms and creatine kinase level above 10 × upper limit of normal; any side effect: composite of any side effect, myalgia and/or creatine kinase level above 3 × upper limit of normal.

^aThe odds ratios (OR) compare carriers versus non-carriers of HLA-B*5701 for abacavir and CC/CT versus TT genotype at SLCO1B1 rs4149056 for simvastatin.

^bBecause the sensitivity is 100%, an adjusted cross table in which 0.5 was added to all cells was used for the calculation of the OR;^{42, 43} measures in bold were reported in the cited scientific articles.