I have an (offline) advertising campaign that I'm running in one city. I'm trying to figure out how to answer the following questions:
What are the chances that the advertising campaign has no positive effect?
What are the chances that the advertising campaign increased sales by at least X%?
I have historical monthly data for the sales going back 6 months. Given that these are small samples, what are the best statistics to use here? I expect the advertising campaign to have a significant effect, so ideally I'd like to be able to say something even with one new data point (one month of data.)