我正在使用面板数据,我想估计一个具有特定状态趋势的固定效应回归。
在Stata,我可以通过以下方式实现这一目标,
xi i.state i.year i.state*time
reg y x _I*
以上将创建状态假人,年假人和50(状态x时间)假人,其中时间以数字方式识别趋势(即1,2,3 ......)
在R中,我可以使用plm或lm运行固定效果模型,例如,
plm(y ~ x, index = c("state", "year"), effect = "twoways", data = df)
lm(y ~ x + factor(state) + factor(year), data = df)
我如何在Stata中以xi的方式包含50(状态x时间)假人?
我知道interaction()
不是我想要的,因为它会创建一个具有n个级别的新因子变量,其中n =(状态数)x(时间段数)。我尝试做的是创建50(状态x时间)变量,使state1xtime为1,2,3 ...当state == 1时为零,否则为zero,对state2xtime重复,其中state == 2,等等
答案 0 :(得分:2)
您只需将state
与year
进行交互即可。正确的运算符是:
,它仅包括交互项。
请注意,lm
和plm
之间存在细微差别:
state:year
state:as.integer(year)
也是如此(执行state:year
会为您提供状态和年份的所有组合)。 检查:
library(plm)
data("Produc", package = "plm")
produc_plm <- pdata.frame(Produc, index = c("state","year"))
### simple state-specific time trend ###
fe1_Ttrend_lm <- lm(log(gsp) ~ -1 + log(pcap) + log(pc) + log(emp) + unemp + state +state:year, data = Produc)
fe1_Ttrend_plm <- plm(log(gsp) ~ log(pcap) + log(pc) + log(emp) + unemp + state : as.integer(year), data = produc_plm)
summary(fe1_Ttrend_lm)$coef[1:4,]
summary(fe1_Ttrend_plm)$coef[1:4,]
答案 1 :(得分:1)
这可能是你想要的:
dta <- data.frame(state = rep(LETTERS[1:3], 10),
time = rep(1:3, each = 10))
dta <- cbind(dta, model.matrix( ~ state - 1, data = dta) * dta$time)
head(dta, 1)
# state time stateA stateB stateC
# 1 A 1 1 0 0
tail(dta, 1)
# state time stateA stateB stateC
# 30 C 3 0 0 3
答案 2 :(得分:0)
要完成Matifou的回答,您还可以使用软件包fixest
:
library(fixest)
data("Produc", package = "plm")
fe_fixest = feols(log(gsp) ~ log(pcap) + log(pc) + log(emp) + unemp + year::state | state, data = Produc)
# Notice the double colon (on the left the numeric variable, on the right the factor). The alternative also works,
# fe_fixest = feols(log(gsp) ~ log(pcap) + log(pc) + log(emp) + unemp + interact(year, state) | state, data = Produc)
# fe_fixest = feols(log(gsp) ~ log(pcap) + log(pc) + log(emp) + unemp + i(year, state) | state, data = Produc)
# Requesting ("standard" standard-errors, otherwise, clustered at state level by default)
coeftable(fe_fixest, se = "standard")[1:4, ]
请注意,如果您不关心交互系数的标准误差,则可以使用以下语法将其投影出来:
fe_fixest_bis = feols(log(gsp) ~ log(pcap) + log(pc) + log(emp) + unemp | state[year], data = Produc)
# state[year] means 'state' fixed-effects and 'state x year' interactions
# The interacted terms are projected out, and the estimation is faster
coeftable(fe_fixest_bis, se = "s")