paired <- NA
unpaired <- NA

for (i in 1:1000) {
  twenty12 <- rnorm(mean=100, n=100, sd=10)
  twenty18 <- rnorm(mean=101, n=100, sd=10)
  paired[i] <- t.test(twenty12, twenty18, paired = T, var.equal = T)$p.value
  unpaired[i] <- t.test(twenty12, twenty18, paired = F, var.equal = T)$p.value
}
plot(paired, unpaired, main = "P values of paired and unpaired T-tests if there is no dependence")

paired <- NA
unpaired <- NA

for (i in 1:1000) {
  twenty12 <- rnorm(mean=100, n=100, sd=10)
  twenty18 <- twenty12+1+rnorm(n=100, sd=10)
  paired[i] <- t.test(twenty12, twenty18, paired = T, var.equal = T)$p.value
  unpaired[i] <- t.test(twenty12, twenty18, paired = F, var.equal = T)$p.value
}
plot(paired, unpaired, main = "P values of paired and unpaired T-tests if there is dependence")