To what extent is this a study of the effectiveness of Facebook/Direct Mail advertising? From the referenced study (https://papers.ssrn.com/sol3/papers.cfm?abs

To what extent is this a study of the effectiveness of Facebook/Direct Mail advertising? From the referenced study (https://papers.ssrn.com/sol3/papers.cfm?abstract_id=4502329 https://papers.ssrn.com/sol3/papers.cfm?abstract_id=4502329): "In the first phase, we used postcards and targeted Facebook advertisements to offer treated individuals free, 13-week online subscriptions to their local newspaper."