i'm not sure how to google for this as i am not very familiar with time series analysis.
i have 500 websites, and i am measuring the number of visitors to each website each day. at some point, i turn on SEO (search engine optimization) for each of the websites. this happens on different days for different websites. the distribution of visitors by account for any given day has a long tail to the right. SEO may not have an immediate effect; it might take a few days/weeks to really start to see some results.
i want to measure something like the "average" lift in the number of visitors, but an average is probably not going to do the trick because of the mix of websites. (a daily/weekly/monthly trend curve would be really cool, but the average problem will exist there, too)
i can probably average the number of visitors per day for any given account, but i can't do it across accounts.
do i simply need to segment the websites into "number of visitor" groups? what other kinds of approaches should i read about?