x <- 1:30 
y <- seq(1, 300, 10) + rnorm(30) 

y[5] <- y[5] + 1989
y[10] <- y[10] + 6
y[25] <- y[25] - 4
fit <- lm(y ~ x)
plot(fit)

y[5] <- y[5] + 2005
y[10] <- y[10] + 2
y[25] <- y[25] - 14
fit <- lm(y ~ x)
plot(fit)

y[5] <- y[5] + 1991
y[10] <- y[10] + 12
y[25] <- y[25] - 28
fit <- lm(y ~ x)
plot(fit)

y[5] <- y[5] + 114
y[10] <- y[10] + 514
y[25] <- y[25] - 55
fit <- lm(y ~ x)
plot(fit)

y[5] <- y[5] + 1
y[10] <- y[10] + 2
y[25] <- y[25] - 3
fit <- lm(y ~ x)
plot(fit)