ggplot(sitios, aes(x = as.factor(x), y = (y))) +
  geom_boxplot(lwd = 0.5, color="black", outlier.colour = "blue",
  outlier.shape = 2) +
  scale_x_discrete(name = NULL, limits=c("a", "b", "c", "d")) +
  theme(axis.text.x = element_text(size = 20, vjust = 1)) +
  scale_y_continuous(name = "y", limits = c(3,5)) +
  stat_summary(fun.y = mean, geom = "point", size = 2.5, shape = 1) +
  theme_classic()