Add measurement error simulation code into book

[vasishth]

Source: https://statmodeling.stat.columbia.edu/2024/04/14/simulation-to-understand-measurement-error-in-regression/#comment-2359176

library(tidyverse)
set.seed(123)
n <- 1000
a <- 0.2
b <- 0.3
sigma <- 0.5

fake %
mutate(y_star = rnorm(n, y, sigma_y),
x_star = rnorm(n, x, sigma_x))

bind_rows(
tibble(x=fake$x, y=fake$y, name=”No measurement error”),
tibble(x=fake$x, y=fake$y_star, name=”Measurement error on y”),
tibble(x=fake$x_star, y=fake$y, name=”Measurement error on x”),
tibble(x=fake$x_star, y=fake$y_star, name=”Measurement error on x and y”)
) %>%
mutate(name = fct_inorder(name)) %>%
ggplot(aes(x,y)) +
geom_point() +
geom_smooth(method=”lm”, fullrange=TRUE) +
facet_wrap(~name)