Net loss function

Adapted from:

1. Bhatt et al, 2015

2. Bertozzi-Villa et al, 2021 (Under review)

net_loss(t, k = 18, l = 8.5)

Arguments

t	Time (years)
k	Rate (fixed from paper)
l	Time at which all nets = 0 (l is estimated so that half_life = 1.64 years (median retention span across all countries))

Value

Proportion of nets retained