clarification about model input parameters

[RiccardoBarb]

Hello, I have a couple of really basic questions concerning the input variables of the model.

1. Is it correct that media_data contains impressions or clicks for each channel but NOT the corresponding costs?
2. Concerning the costs variable, is it to be considered a single vector tracking the global costs (the sum of each channel spend) or rather a matrix with a column for each channel spend?
3. Are the costs to be intended as absolute values, such as the spend for a specific channel o a given day/week, or rather the cost per thousand impressions / cost per click / marketing cost per unit?

Cheers

[pabloduque0]

Hello @RiccardoBarb !

1. Media data can contain impressions, clicks or spend (cost). But if is indeed impressions or clicks it wont contain cost as you said.
2. A single vector indicating the total cost of the channel in the data.
3. When we talk about costs we refer total costs. For optimisation and other parts we refer to price as the price per unit of an impression/click.

Hope it helps! Let me know if anything needs further clarification!

[RiccardoBarb]

hi @pabloduque0 thanks for your response!

What would be the recommended variable to use for media_data? would it be better to use spend or clicks/impressions?.
Also if I decide to use spend as media_data, then wouldn't cost be redundant information? would it still be needed to fit the model?
As far as the second answer is concerned, what if I have multiple media channels? Should I insert a single vector for each channel (which, in this case, is in fact equivalent to a matrix)?

Thanks

[pabloduque0]

Between clicks and impressions, impressions are preferred.

In reality the costs are used for the media prior (if you are referring to mmm.fit(..., media_prior=costs) therefore costs are still relevant as they serve as the prior. If you want to use a different prior then you mostly wont need costs. The only place where costs are "mandatory" is for ROI calculation (for obvious reasons).

Apologies if that was not clear before, what I mean is a single vector indicating the total cost each channel in the data, with ONE value per channel, so the total costs. So always one vector with one value per media channel. Eg. for three channels your costs could be jnp.array([1, 2, 3]).

[RiccardoBarb]

Thanks a lot @pabloduque0 it's much clearer now :)

Cheers