Today, smallpox, polio, typhoid and measles are no longer common because most people
参考例13.9并利用CRIME4.RAW中的数据。
(i)假定你在做差分以消除非观测效应后, 认为log(pol pc)与log(crm rte) 是同时决定的; 特别是犯罪的增加与警察人数的增加有关。这对解释方程(13.33)中log(pol pc) 的正系数有何帮助?
(ii)变量tca pc表示全县人均征税量。将它排除在犯罪方程之外看上去合理吗?
(iii)在包括了潜在的工具变量log(tap c)后, 利用混合OLS估计log(pol pc) 的约简型。log(tax pc) 看起来是一个很好的备选IV吗?
(iv)假设在几年后,北卡罗来纳州资助某些县扩大其警察规模。你如何利用这个信息估计增加的警察对犯罪率的影响?
A.possibility;necessity
B.impossibility;necessity
C.possibility;unnecessity
D.impossibility;unnecessity
In today’s society, people are ()for different reasons, such as, their achievement, their wealth, or even their appearance.
A、celebrated
B、congratulated
C、prized
D、encouraged
A.courses
B.plates
C.foods
D.dishes
A.Must, can’t
B.Must, needn’t
C.May, needn’t
D.Can, mustn’t
A.despite
B.but
C.even
D.except
A、It is a sunny day
B、I like sunny day
C、I hate it
A、this morning
B、today in the morning
C、today morning
D、in the morning today
A.or
B.on
C.both
D.either