```
# NOT RUN {
## data and transformed variables
data("Journals")
journals <- Journals[, c("subs", "price")]
journals$citeprice <- Journals$price/Journals$citations
journals$age <- 2000 - Journals$foundingyear
journals$chars <- Journals$charpp*Journals$pages/10^6
## Stock and Watson (2007)
## Figure 8.9 (a) and (b)
plot(subs ~ citeprice, data = journals, pch = 19)
plot(log(subs) ~ log(citeprice), data = journals, pch = 19)
fm1 <- lm(log(subs) ~ log(citeprice), data = journals)
abline(fm1)
## Table 8.2, use HC1 for comparability with Stata
fm2 <- lm(subs ~ citeprice + age + chars, data = log(journals))
fm3 <- lm(subs ~ citeprice + I(citeprice^2) + I(citeprice^3) +
age + I(age * citeprice) + chars, data = log(journals))
fm4 <- lm(subs ~ citeprice + age + I(age * citeprice) + chars, data = log(journals))
coeftest(fm1, vcov = vcovHC(fm1, type = "HC1"))
coeftest(fm2, vcov = vcovHC(fm2, type = "HC1"))
coeftest(fm3, vcov = vcovHC(fm3, type = "HC1"))
coeftest(fm4, vcov = vcovHC(fm4, type = "HC1"))
waldtest(fm3, fm4, vcov = vcovHC(fm3, type = "HC1"))
## changes with respect to age
library("strucchange")
## Nyblom-Hansen test
scus <- gefp(subs ~ citeprice, data = log(journals), fit = lm, order.by = ~ age)
plot(scus, functional = meanL2BB)
## estimate breakpoint(s)
journals <- journals[order(journals$age),]
bp <- breakpoints(subs ~ citeprice, data = log(journals), h = 20)
plot(bp)
bp.age <- journals$age[bp$breakpoints]
## visualization
plot(subs ~ citeprice, data = log(journals), pch = 19, col = (age > log(bp.age)) + 1)
abline(coef(bp)[1,], col = 1)
abline(coef(bp)[2,], col = 2)
legend("bottomleft", legend = c("age > 18", "age < 18"), lty = 1, col = 2:1, bty = "n")
# }
```

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