Constructing a demographic function from population values and indicators. The demographic function (solid line) is a piecewise linear function whose X axis points (time) are a subset of the set of all coalescent times, and whose Y axis values (population size) are the value of the population parameter (θ) at this point. Time starts at zero (the present) increases as we move further into the past. The indicator parameter (λ) determines the subset to use for the X axis. In the instance shown above only three of the six population values are used. λ4 = λ5 = 1, λ1 = λ2 = λ3 = 0.
Heled and Drummond BMC Evolutionary Biology 2008 8:289 doi:10.1186/1471-2148-8-289