A survey was conducted on 193 Duke University undergraduates who took an introductory statistics course in 2012. Among many other questions, this survey asked them about their GPA, which can range between 0 and 4 points, and the number of hours they spent studying per week. The scatterplot below displays the relationship between these two variables.

Solution

a) What is the explanatory variable and what is the response variable?

The explanatory variable is study hours per week and the response variable is the GPA.

b) Describe the relationship between the two variables. Make sure to discuss unusual observations, if any.

There seems to be a positive association, that is, that the more study hours, the higher the GPA.

Some unusual observations are: there is a person with a GPA above 4, but 4 should be the limit.

There are two people that claimed to study more than 60 hours per week.

c) Is this an experiment or an observational study?

It is an observational study

d) Can we conclude that studying longer hours leads to higher GPAs?

We can’t because it is an observational study, we can just point to an association (or correlation).