Table 4. Estimated predictive values of the two tests in the four sub-populations (Test 1 = T. brucei s.l. specific PCR; test 2 = T. brucei s.l. ITS-PCR).

Sub-population	Prevalence	PPV	PPV	NPV	NPV
		Test 1	Test 2	Test 1	Test 2
cattle	0.091	0.970	0.950	0.976	0.965
goats	0.005	0.625	0.505	0.999	0.998
pigs	0.066	0.957	0.929	0.983	0.975
sheep	0.006	0.659	0.534	0.998	0.998

PPV is the positive predictive value of the test at a given prevalence i.e. how likely the animal is to have the pathogen given that it has a positive test result. NPV is the negative predictive value of the test at a given prevalence i.e. how likely is an animal not to have the pathogen given that it had a negative test result.