# Statistics Lab / ferdo — synthetic data (no real student records)
# Save stats_synthetic.csv in your working directory.
d <- read.csv("stats_synthetic.csv", stringsAsFactors = TRUE)
stopifnot(nrow(d) == 36, all(c("score_pre","score_post","group") %in% names(d)))
# Groups are observational labels: differences cannot establish a treatment effect.

d <- read.csv("stats_synthetic.csv")
str(d)
sapply(d, function(x) sum(is.na(x)))
table(d$stress_rating, useNA = "ifany")
# Do not replace NA with 0 without justification.