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Adding an outbreak

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    Leonardo FridLeonardo Frid

    Hi Josh,

    If your outbreaks are correlated between strata, I think the best you could do is create an external variable for outbreak years (0/1) and define a value for this for every iteration/timestep. This would reduce the number of records you have to define somewhat but not entirely. To do it, here are the steps I would follow:
    1. Create an external variable under Project Properties: “Outbreak Year”
    2. Create a Distribution Type under Project Properties: “Outbreak Multiplier”
    3. Under Scenario Properties | External Variables:Define a value for each timestep and iteration that includes the 0 values for non outbreak years and the 1 values for outbreak years.
    4. Under Scenario Properties | Distributions you would then define two Distribution records for each stratum that specify the “Outbreak Multiplier” when your “Outbreak Year” value is 0 and the other when it is 1. Set the Sampling frequency to “every timestep”.
    5. Under Scenario Properties | Transitions – Multipliers set your multipliers to come from the “Outbreak Multiplier” Multiplier Distribution. Set the Sampling frequency to “every timestep”.

    Hope that helps!

    Leonardo FridLeonardo Frid

    One additional note is that for outbreak/non-outbreak years in your external variable, you don’t need a record for every timestep. For example if you had a 7 year outbreak starting in 2020 followed by a 20 year non-outbreak period your external variable records would be:
    Iteration, Timestep, Value
    1, 2020, 1
    1, 2027, 0
    1, 2047, 1

    This will also greatly reduce the number of records that you need.



    Thanks for the explanation, Leonardo. Unless I am missing something, I think the main limitation of the approach you describe are:

    1) I would still need to use some sort of random number generator to figure out when an outbreak would occur within an iteration (but I think I could work around this), and
    2) The approach seems a bit time consuming when each iteration contains hundreds to thousands of timesteps, like in a natural/historical range of variability analysis.

    But I look forward to using the approach you describe in shorter runs down the road. Again, thanks for making the time to answer my original question.


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