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In this lesson, we will learn how to differentiate between surveys, experiments, and observational studies.

Q1:

A solar panel manufacturer plans to carry out an experiment to investigate how two different transparent protective coatings deposited on solar panels affect their efficiency.

Which of the following is the treatment variable in this experiment?

Which of the following is the response variable in this experiment?

Q2:

Which of the following statements about blocked experiments is NOT true?

Q3:

Mariam wants to redecorate her bedroom. She has found two different blue paints for the door. She wants to test which of them, once dry, gives the closest colour to that of her bed frame.

Q4:

A real estate agency have found some volunteers to test two different website designs. They have grouped the volunteers in pairs so that, in each pair, both participants have the same characteristics in terms of gender, age, IT skills, and experience with property search. Then, they randomly assign one website to be tested to one participant in each pair and the other website to the other participant. What is this type of experiment design called?

Q5:

Sameh wants to know if his new idea for a bread recipe will indeed improve his homemade bread. He invites a group of friends to a brunch at his house. He gives half of them the bread made according to the old recipe first and then the bread made with the new recipe, while the other half of his friends get the two different bread in the reverse order. What is this type of experiment design called?

Q6:

The owner of a fitness club wants to investigate whether eating a yogurt whose composition is specially designed for sports people increases their performance. She notices that the members of her club have different characteristics in terms of age and level of sports practice in general.

She wants to find out what proportion of her club’s members already eat this yogurt regularly by surveying a sample of members. She thinks a proportional stratified sample would be a suitable technique. Which of the following statements about her stratified sample is not true?

The club owner now wants to investigate the effect of eating this ‘special’ yogurt. She sends an email to all her club’s members, calling for volunteers among people who have never tried this yogurt. No less than 76 members have volunteered. As she has identified age and level of sports practice as possible confounding variables, she groups her volunteers according to 12 subcategories given by four age groups and three levels of sports practice. She then randomly splits each group into two halves and gives to one of them a diet based on this yogurt and to the other half a diet based on a placebo (i.e., a ‘normal’ yogurt but with the same label as the previous one).

What is the treatment variable in this experiment?

The club owner used a measure of fitness performance before and after the diet and then analyzed how this measure changed with or without the ‘special’ yogurt for each subcategory. What is this type of experiment design called?

Q7:

Education scientists thought of a new way to teach a certain topic. They decided to test the effectiveness of their method by teaching the topic in the traditional way to a given group of students and in the new way to another group of students and then compare the performance of both groups of students at a task related to the taught topic.

Many variables need to be controlled in order to make their experiment results valid. Which of the following variables does NOT need to be controlled?

Not telling the students that they are taking part in an experiment makes it a blind experiment. If they wanted to make a double-blind experiment, what would be necessary?

Q8:

Karim wants to investigate whether mud on his sweater is better washed out when the stains are first rubbed with soap or when soaked overnight in clean water.

Q9:

A positive correlation has been observed between the amount of sun cream sold and the occurrence of skin cancer.

Do you believe one can conclude that sun cream causes skin cancer?

Which of the following could be the lurking variable here?

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