Experimental vs. Observational Studies

Experimental vs. Observational Studies

Multiple Choice

A principal wants to know how teachers feel about changes to their schedule. He decides to ask a sample of 20 teachers. Classify each sampling method.

Randomly choose 2 teachers from each of the school’s 10 departments of various sizes.

• Simple Random

• Systematic

• Stratefied

• Cluster

Multiple Choice

A principal wants to know how teachers feel about changes to their schedule. He decides to ask a sample of 20 teachers. Classify each sampling method.

Survey the first 20 teachers who volunteer.

• Simple Random

• Self-Select

• Cluster

• Stratefied

Multiple Choice

A principal wants to know how teachers feel about changes to their schedule. He decides to ask a sample of 20 teachers. Classify each sampling method.

Randomly choose 20 teachers from an alphabetical list of the 60 teachers in the school.

• Cluster

• Convenience

• Systematic

• Simple Random

Vocabulary

• Statistic: a number that describes a sample (s and s)

• Parameter: a number that describes a population (p and p)

Multiple Select

In a survey of 50 students at a high school, 32 students said that they plan to attend the homecoming dance. The school has 720 students.

Which number is a statistic? Which number is a parameter?

• Statistic: 50

• Statistic: 720

• Parameter: 720

• Parameter: 50

Multiple Choice

In a survey of 50 students at a high school, 32 students said that they plan to attend the homecoming dance. The school has 720 students.

Predict the number of students who plan to attend the homecoming dance. (Hint- set up a proportion and cross multiply)

• 460

• 460.8

• 461

• 400

Multiple Select

In a random sample of phone calls to a police station, 11 of the 25 calls were for emergencies. Suppose the police station receives 175 calls in one day.

What number is a statistic? What number is a parameter?

• Statistic: 25

• Statistic: 175

• Parameter: 25

• Parameter: 175

Open Ended

Example 2: In a random sample of phone calls to a police station, 11 of the 25 calls were for emergencies. Suppose the police station receives 175 calls in one day. Predict the number of calls that

will be for emergencies

Vocabulary

• Experiment: imposes treatment on individuals to collect data on their response treatment.

• Ex: test to see how well plants grow in light

• Observational Study: observes individuals and measures variables without controlling the individuals or their environment in any way

• Ex: you want to see if poor nutrition affects eyesight- it would be unethical to force someone to have poor nutrition

Poll

Experiment or Observational Study?

A researcher asks students the average number of hours of sleep they get per night and examines whether the amount of sleep affects students’ grades.

• Experiment

• Observational Study

Poll

Experiment or Observational Study?

A park employee wants to know if latex paint is more durable than non-latex paint. She paints 50 benches with latex paint, and 50 with non-latex paint.

• Experiment

• Observational Study

Poll

Experiment or Observational Study?

A scientist measures the height of 20 birds’ nests, and counts the number of eggs to see if there is a relationship.

• Experiment

• Observational Study

Vocabulary

• Controlled experiment: two groups are studied under conditions that are identical except for one variable

• Treatment group: group that receives treatment

• Control group: group that does not receive treatment, used for comparison

Describe the treatment, the treatment group, and the control group. 

At Ashland Middle School, fifty randomly chosen students were given milk, as normal, at lunch every day for a year, and fifty other randomly chosen students were given other beverages.

Describe the treatment, the treatment group, and the control group. 

To test the redesign of its Web site, an online bookseller assembled 96 users of the site and randomly divided them into two groups. One group used the new Web site to make an online purchase and one group used the old Web site to do the same transaction.

Poll

Explain whether the research topic is best addressed through an experiment or an observational study.

Does listening to a music player with earphones for more than one hour per day affect a person’s hearing?

• Experiment

• Observational Study

Poll

Explain whether the research topic is best addressed through an experiment or an observational study.

Do people who consume 1000 milligrams of vitamin C each day as a dietary supplement have lower cholesterol levels than people who do not consume vitamin C supplements?

• Experiment

• Observational Study

Open Ended

A researcher is considering three methods of evaluating two different cold medicines. Tell whether each method is a survey, an experiment or an observational study.

Choose 50 people at random. Ask which cold medicines they have taken in the past, and how effective they were.

Open Ended

A researcher is considering three methods of evaluating two different cold medicines. Tell whether each method is a survey, an experiment or an observational study.

Monitor 50 people with colds, and measure the length of the symptoms for the individuals who choose to take each type of medicine.

Open Ended

A researcher is considering three methods of evaluating two different cold medicines. Tell whether each method is a survey, an experiment or an observational study.

Randomly divide a group of 50 people with colds into two groups. Give each group a different medicine, and measure the length of the symptoms.

Open Ended

What is the difference between a survey, an experiment, and an observational study?