A small local umbrella company is trying to test the effectiveness of their umbrellas by looking at how many umbrellas they sell each year.

In 2014, the company sold 2,000 umbrellas.

In 2015, they sold 1,500 umbrellas.

They assume that their umbrellas are less effective which is why sales decreased.

However, there could be many confounding factors. Which of the following is NOT a possible confounding factor?

An experiment testing the effects of caffeine on endurance performance in athletes assigns caffeine to a randomly selected group of athletes and has them exercise. Another trial was conducted in which the same group exercised without anything given to them to take. The results did not match the expected results. What should be done to improve this experiment?

An experiment was done by medical researchers to determine the association between drinking caffeine and severity of lung cancer. Results showed that there was a high association between the two variables. Which of the following could be a potential confounding variable in the experiment?

A study finds that caffeine intake has a strong positive correlation with grades for college students. In other words, on average, the more caffeine intake a student has, the higher a grade the student gets.

Which of the following could potentially be a confounding variable in this experiment?

Let us suppose a company wants to evaluate whether a new medical device works better than current devices. It conducts a small experiment to assess the effectiveness of the new device. To conduct the experiment, the company randomly assigns one group to the new medical device, which requires users to stay well hydrated, and the other group to the old device.

How should we control for confounding variables?