Table 1.

Models of the equilibrium relationships between the proportion (P) of cattle plus farmed deer herds with bovine TB at 30 June each year and annual possum (V) control costs and annual disease (D) control costs during the previous 12 months

Number	Model	Diminishing returns?	Asymptote?
1	P = a + bV	No	No
2	P = a + (b/V)	Yes	Yes (a)
3	P = a + bD	No	No
4	P = a + (b/D)	Yes	Yes (a)
5	P = a + b(V + D)	No	No
6	P = a + (b/(V + D))	Yes	Yes (a)

Models 2, 4 and 6 assume that control costs are greater than 0 and show diminishing returns and an asymptote (a).