This task is about reading the given passage and construct a question about the information present in the passage. Construct a question in such a way that (i) it is unambiguous, (ii) it is answerable from the passage, (iii) its answer is unique (iv) its answer is a continuous text span from the paragraph. Avoid creating questions that (i) can be answered correctly without actually understanding the paragraph and (ii) uses same words or phrases given in the passage.

An investigation by ProPublica found that at least 21 doctors have been paid more than $500,000 for speeches and consulting by drugs manufacturers since 2009, with half of the top earners working in psychiatry, and about $2 billion in total paid to doctors for such services. AstraZeneca, Johnson & Johnson and Eli Lilly have paid billions of dollars in federal settlements over allegations that they paid doctors to promote drugs for unapproved uses. Some prominent medical schools have since tightened rules on faculty acceptance of such payments by drug companies.
Who conduced an investigation on doctors?