Formative Check - Intro to Experiments

A researcher wants to test whether the amount of sleep before a test affects student test scores.
What is the explanatory variable?

• The students who took the test

• The number of hours of sleep before the test

• The difficulty of the test

• The test scores

Answer explanation

Rationale: The explanatory variable is what we think explains or influences the outcome. In this case, it’s the amount of sleep. The response variable is the test score.

Tags

CCSS.HSS.IC.B.3

In a study testing if fertilizer type affects plant growth, what is the response variable?

• Type of fertilizer used

• Amount of water given

• Height of the plants after 4 weeks

• Number of plants in the study

Answer explanation

Rationale: The response variable is what is measured — plant growth. Fertilizer type is the explanatory variable.

Tags

CCSS.HSS.IC.B.3

A school surveys 50 students to learn about all 1,200 students’ opinions on the cafeteria food.
What is the population?

• The 50 students surveyed

• All 1,200 students in the school

• All students who eat lunch

• The cafeteria staff

Answer explanation

Rationale: The population is the entire group we want information about (all students). The sample is the 50 surveyed.

Tags

CCSS.7.SP.A.1

CCSS.HSS.IC.A.1

A study finds that students who study while listening to music tend to have higher grades. Which is the most likely confounding variable that could explain this result?

• The type of music students listen to

• Students who listen to music while studying may also study for longer periods of time

• The volume level of the music

• Students who listen to music may also have quieter home environments

Answer explanation

Rationale: The study seems to show music causes higher grades, but maybe those students actually spend more time studying (a lurking variable). D is also tempting, but B is more directly related to study habits.

Why is random assignment of subjects to treatment groups important in an experiment?

• It guarantees larger sample sizes

• It ensures results apply to the entire population

• It reduces the chance that pre-existing differences between groups affect the results

• It makes the study faster to complete

Answer explanation

Rationale: Random assignment balances out differences between groups so that the only real difference is the treatment.

Why do researchers often include a control group in an experiment?

• To have more participants overall

• To give every participant the treatment at least once

• To compare the treatment results to what happens without the treatment

• To guarantee the treatment will work

Answer explanation

Rationale: A control group is the baseline for comparison, showing what would happen without the new treatment.

Why is it important to have many experimental units (subjects) in a study?

• Larger studies always prove the hypothesis true

• It increases the chance that results are due to random variation

• It makes it more likely the results are reliable and not just due to chance

• It guarantees the sample represents the population

Answer explanation

Rationale: Larger sample sizes reduce the influence of random variation and strengthen the reliability of conclusions.

Tags

CCSS.HSS.IC.B.3