# 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.

plot(d$study_hours, d$score_post, pch=19,
     xlab="Study hours", ylab="Post-quiz score")
cor(d$study_hours, d$score_post, method="pearson")
cor(d$study_hours, d$score_post, method="spearman")
cor.test(d$study_hours, d$score_post)