Expirimental Design

Runners after an ultramarathon commonly develop respiratory infections. We want to know if taking 600 milligrams of vitamin C daily will reduce these infections. Researchers randomly assigned 100 ultramarathon runners to receive either vitamin C or placebo. All subjects were watched for 14 days after the big race to see if infections developed. What are the possible lurking variables?

• Age of the runner
• weight of the runner
• gender of the runner
• all of the above

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CCSS.HSS.IC.B.3

Runners after an ultramarathon commonly develop respiratory infections. We want to know if taking 600 milligrams of vitamin C daily will reduce these infections. Researchers randomly assigned 100 ultramarathon runners to receive either vitamin C or placebo. All subjects were watched for 14 days after the big race to see if infections developed. The type of design used here?

• matched pairs
• randomized block
• completely randomized
• stratified 

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CCSS.HSS.IC.B.3

Can pleasant aromas help a student learn better? Two researchers believed that the presence of a floral scent could improve a person's learning ability in certain situations. They had 22 people work through a pencil-and-paper maze 6 times. Three of the times they wore a floral-scented mask and three times they wore an unscented mask. The three trials for each mask followed one another. Testers measures the length of time it took subjects to complete each of the six trials. They reported that, on average, subjects wearing the floral-scented mask completed the maze more quickly that those wearing the unscented mask, although, the difference was not statistically significant. This study is:

• a convenience sample
• an oberservational study
• an experiment, but not double-blind
• a double-blind experiment

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CCSS.HSS.IC.B.3

The most important advantage of experiments over observational studies is that

• A) experiments are usually easier to carry out
• B)Experiments can usually give better evidence of causation
• C) Confounding cannot happen in experiments
• D) Observational studies cannot use random samples

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CCSS.HSS.IC.B.3

In order to perform an experiment using 60 members of a gym, I first divide the list of members into men and women because I feel that the results will be different based on gender. I then randomly choose 30 men and 30 women. I assign half of the men to the treatment group and half to the control group. I repeat this procedure with the women. This is an example of a:

• randomized comparative design
• blocking design
• matched pairs design
• double blind simple random sample

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CCSS.HSS.IC.B.3

A market research company wishes to find out whether the population of students at a university prefers Starbucks or Dunkin Donuts. A random sample of students is selected, and each student is asked first to try both but the order they try them is randomly decided with a coin toss (heads: Starbucks, then Dunkin. tails: vice versa). They then indicate which brand they prefer. This is an example of

• a completely randomized experiment
• an observational study
• a stratified sample
• a matched pairs experiment

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CCSS.HSS.IC.B.3

Why do we randomize in an experiment or a survey?

• Because we have to
• It helps reduce the effects of confounding variables
• It eliminates all possible confounding variables
• It makes sampling easier

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CCSS.HSS.IC.B.3

Identify the design  for the experiment

• completely randomized, the factor is pesticide
• randomized block, blocked on tree type, the factor is pesticide
• This experiment is single blind, blocked by pesticide
• The experiment is double blind, the factors are tree type and pesticide

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CCSS.HSS.IC.B.3

Do cars get better gas mileage with premium instead of regular gasoline?

If you were doing this experiment, what are some variables you could block with to address potential confounding variables? Choose all that apply.

• Type of car

• Age of car

• Engine size

• Make (Brand of car)

• Car color

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CCSS.HSS.IC.B.3

A reading specialist in a large public school system believes that the more time students spend reading, the better they will do in school. She plans a middle school experiment in which an SRS of 30 eighth graders will be assigned four extra hours of reading per week, and SRS of 30 seventh graders will be assigned two extra hours or reading per week, and an SRS of 30 sixth graders with no extra assigned reading will be a control group. After one school year, the mean GPAs from each group will be compared. Is this a good experimental design?

• Yes

• No, because while this design may point out an association between reading and GPA, it cannot establish a cause-and-effect relationship.

• No, because without blinding, there is a strong chance of a placebo effect.

• No, because any conclusion would be flawed because of blocking bias.

• No, because grade level is a lurking variable which may well be confounded with the variables under consideration.

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CCSS.HSS.IC.B.3