In Example 13.8, we used the unemployment claims data from Papke (1994) to estimate the effect of enterprise zones on unemployment claims. Papke also uses a model that allows each city to have its own time trend. log(uclmst) = ai + cit + β1ezit + uit ,
where ai and ci are both unobserved effects. This allows for more heterogeneity across cities.
(i) Show that, when the previous equation is first differenced, we obtain
△log(uclmsit) = ci + β1△ezit + △uit, t = 2,..., T.
Notice that the differenced equation contains a fixed effect, ci.
(ii) Estimate the differenced equation by fixed effects. What is the estimate of β1? Is it very different from the estimate obtained in Example 13.8? Is the effect of enterprise zones still statistically significant?
(iii) Add a full set of year dummies to the estimation in part (ii). What happens to the estimate of β1?

Alandowner and his neighbor purchased adjoining undeveloped lots. after both built homes on their respective lots, the landowner suggested to the neighbor that a common driveway be built where the two lots joined. the neighbor agreed. the landowner and the neighbor split the cost of constructing the driveway and entered into a written agreement to equally share the costs of its upkeep and maintenance. the agreement was recorded in the county recorder's office. two years later, the neighbor built a new driveway located entirely on his lot. the common driveway, which the landowner continued to use but which the neighbor no longer used, began to deteriorate. the landowner asked the neighbor for money to maintain the common driveway, but the neighbor refused to contribute. three years later, the neighbor conveyed his lot to a friend. the friend entered into possession and used only the driveway built by the neighbor. by this time, the common driveway had deteriorated badly and contained numerous potholes. the landowner asked the friend to pay half of what it would take to repair the common driveway. the friend refused. the landowner repaired the driveway and sued the friend for 50% of the cost of repairs. will the landowner prevail?

Asmartphone manufacturing company uses social media to achieve different business objectives. match each social media activity of the company to the objective it the company achieve.

%of the world's population controls approximately % of the world's finances (the sum of gross domestic products)" quizlket