Variable depending on time +delay

[Raquel]

Hi, I'm new to vensim, it may be a basic question

I do have two variables ("media pressure" and "time of remembrance") which are inputs for "desire to donate".
"Desire to donate" should be a sum of "media pressure" (dmnl) for the "time of remembrance" (days).
E.g., if time of remambrance is 4 => desire to donate(T) = media pressure(T-1) + media pressure(T-2) + media pressure(T-3) +media pressure(T-4)
Is that possible? And putting all that in an information delay function?

Grateful for any/every help

[tomfid]

I know exactly what you mean - this sounds like a variation on what marketing science types call an adstock transformation.

You can use a discrete delay, but I'd encourage you to make this a continuous process, because it's more realistic for people to gradually forget media exposure, than to have its effect end abruptly after some time.

Here's one way to do it:

- create a stock of "desire to donate"
- inflow: "creating desire" depends on media exposure
- outflow: "forgetting" = desire/time to forget

This is linear - if you want it nonlinear, to capture saturation, you might instead do:

- stock of cumulative media exposure
- inflow: exposure to messages
- ouflow: forgetting (as above)

Then desire = f(cumulative exposure), with f() as an expression, or a lookup for convenience.

Wish I could say more, but I have to catch a plane. Good luck.

[Raquel]

Thank you, tomfid
It worked perfectly!