Melissa is in the 7th grade. She wanted to know how after-school activities done on the week before an exam affect the score of the exam. She asked all of her classmates to record their after-school activities on the week before a big exam. Later, she compared the records with the achieved scores of each student.

What type of statistical study did Melissa use?

A research institute wanted to test a new method for teaching geometry by assessing whether it helps students achieve higher grades. They decided to conduct a study using 4 volunteering high schools with a total of 750 students.

At the beginning of the semester, 2 out of the 4 high schools were randomly picked to use the new teaching method, while the remaining 2 schools kept teaching with traditional methods. The first pair had a total of 400 students, and the second pair had a total of 350 students. By the end of the semester, the researchers compared the average scores in the geometry section of the final exam for each pair of schools.

What type of statistical study did the researchers use?

A pharmaceutical company wanted to check whether their new cough medicine, “Serenity,” really relieves coughs. To do that, they went over medical records of all clinics in the country and looked for an association between the type of medicine prescribed for patients who suffer from coughs and the level of their recovery. What type of statistical study did the pharmaceutical company use?

We want to determine which brand of orange juice people prefer. A sample is randomly chosen at the supermarket and people in the sample are asked to taste both brands, not being told which they are drinking. Then they will state their preference. What type of statistical study did we use?