Initialising delays
Posted: Sat Nov 15, 2008 12:01 am
As part of a drug treatment model, I am trying to prison sentences. That is, there is a stock of current prisoners and a delay function is needed to control their outflow. Prison sentence durations are right skewed (large number of short sentences, small number of much longer sentences).
In practice, the inflow to the prisoner stock is reasonably constant. As such, despite the varying sentence lengths, the outflow is also pretty constant despite the skewed durations. Thus, my initial thought was to just model as a constant (with some random variation). However, this does not map well to the conceptual view of the world. Thus, I am likely to use DELAY PROFILE.
I can make this delay function do what I want and it seems to behave sensibly if mean delay changes. However, I cannot work out how to initialise it. That is, at the start, there is some number of existing prisoners that need to be released.
I have attached an example that has 0 inflow so the only outflow comes from the initialisation. The stock quickly falls below 0. What am I doing wrong?
thanks, Jen
In practice, the inflow to the prisoner stock is reasonably constant. As such, despite the varying sentence lengths, the outflow is also pretty constant despite the skewed durations. Thus, my initial thought was to just model as a constant (with some random variation). However, this does not map well to the conceptual view of the world. Thus, I am likely to use DELAY PROFILE.
I can make this delay function do what I want and it seems to behave sensibly if mean delay changes. However, I cannot work out how to initialise it. That is, at the start, there is some number of existing prisoners that need to be released.
I have attached an example that has 0 inflow so the only outflow comes from the initialisation. The stock quickly falls below 0. What am I doing wrong?
thanks, Jen