A basic experiment

Let's dive into experimental design. Note that all of these concepts will be covered in more detail in the next video, "Hypothesis Testing."

ToothGrowth is a built-in R dataset from a study that examined the effect of three different doses of Vitamin C on the length of the odontoplasts, the cells responsible for teeth growth in 60 guinea pigs, where tooth length was the measured outcome variable.

Built-in data can be loaded with the data() function. The dataset will be loaded as a data frame with the same name passed as an argument to data(). For example, you can load the famous iris dataset using data("iris").

If you wanted to conduct a two-sided t-test with the famous mtcars dataset, it would look like this, where x is the outcome in question, alternative is set to "two.sided", and mu is the value you're testing to see if the mean of mpg is not equal to.

data(mtcars)

t.test(x = mtcars$mpg, alternative = "two.sided", mu = 40)

Suppose you know that the average length of a guinea pigs odontoplasts is 18 micrometers. Conduct a two-sided t-test on the ToothGrowth dataset. Here, a two-sided t-test will check to see if the mean of len is not equal to 18.

Load the ToothGrowth dataset with the data() function (like shown above.) Run this line and then type ToothGrowth into the console to be sure it loaded.
Use t.test() to test if the len variable is not equal to 18 micrometers (a two-sided t-test.) There is an example above that you should model your code after.

Exercise

A basic experiment

Instructions