The question is: explain differences between ordinary least square and 4 estimate in the given example. in next part test exogenity assumption. then give reasons of breach of exclusion restriction. d part is optional. please see below for details:

Workers working from home and businesses limiting the number of staff on site are among the most important tools that have been used to slow the spread of the SARS-CoV-Z virus. This has taken the form both of individual actions, as workers choose to stay away from the workplace and businesses reduce on-site operations; and government mandates to close down particular types of business or lockdowns or shelter-in-place orders. A recent working paper titled \"Effects of Reduced Workplace Presence on COVlDIQ Deaths: An Instrumental-Variables Approach\" studies how effective staying away from work has been in reducing COVID-lS mortality in the US.3 The paper first shows that, over the period under study, COVID-lQ deaths are higher in US counties with a higher aggregate absence from work. Second, to deal with the potential endogeneity of workplace presence, they use an instrumental variables (IV) strategy based on an index of ability to work from home for each occupation. In particular, the index used as an instrument measures whether workers in a given county are in occupations that enable them to work from home. The IV indicates that moving 10 percent of a county's workers from the workplace would lower deaths by three quarters one month later. (a) Discuss possible explanations for why the OLE estimate differs from the IV estimate in this particular context. [5 marks] In the IV strategy, would you expect the exogeneity assumption to be satisfied? How would you test this assumption? (5 marks] Propose some possible violation of the exclusion restriction. {5 marks) Discuss verbally who are the always-takers, the never-takers, the compiiers, and the defiers. (5 marks}