Holt McDougal Algebra 2 Surveys, Experiments, and Observational studies Holt Algebra 2 Warm Up Warm Up Lesson Presentation Lesson Presentation Lesson Quiz

Holt McDougal Algebra 2

Surveys, Experiments, and Observational studiesSurveys, Experiments, and Observational studies

Holt Algebra 2

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Surveys, Experiments, and Observational studies

Warm UpIdentify the population and the sample.

1. Fifty teenagers are randomly selected and asked whether they have siblings.

population: teenagers; sample: the 50 selected teenagers

2. Fifteen passengers on a flight are asked about the quality of the flight attendants’ service.

population: passengers on the flight; sample: the 15 people asked



3. To determine how many cats have blue eyes, the eye colors of 10 cats at each of 10 animal shelters in different states are recorded.

population: cats; sample: the 100 cats whose eye colors are recorded



Focus on the commonalities and differences between surveys, experiments, and observational studies.

Objectives



experiment

observational study

controlled experiment

control group

treatment group

randomized comparative

experiment

Vocabulary



You have already seen that a survey is one way to collect data. Although surveys are useful, different situations require different techniques for gathering data.Individuals are people, animals, or objects that are described by data. If you collect data on the fuel efficiency of cars and trucks, the individuals are vehicles. Variables are used to describe individuals. Fuel efficiency, measured in miles per gallon, is an example of a variable.





For data from an experiment to be useful, the experiment must be carefully designed. In a controlled experiment, two groups are studied under conditions that are identical except for one variable. The effects of the treatment are determined by comparing the control group and the treatment group.



Often, to demonstrate a cause and effect hypothesis, an experiment must show two things. First, that a phenomenon occurs with the treatment; and second, that the phenomenon does not occur in the absence of the treatment.

In a randomized comparative experiment, the individuals are assigned to the control group or the treatment group at random, in order to minimize bias. An experiment that is not a randomized comparative experiment may be subject to bias, and any conclusions drawn from the experiment may not be valid.



Explain whether each situation is an experiment or an observational study.

Example 1: Identifying Experiments and Observational Studies

A. A researcher wants to know if a soil additive makes a fern grow more quickly. He grows one specimen in treated soil and one in untreated soil.The researcher applies a treatment, so the situation is an experiment.

B. To find out whether car accidents are more likely on rainy days, a researcher records the weather conditions during 50 randomly selected accidents for the past year.



The researcher gathers data without controlling the individuals or applying a treatment. The situation is an example of an observational study.

Continued Example 1: Identifying Experiments and Observational Studies



A scientist measures the height of 20 birds’ nests, and counts the number of eggs to see if there is a relationship. Is this experiment or an observational study? Explain.

Check It Out! Example 1

It is an observational study because an observationis being conducted without controlling the environment in any way



Example 2: Evaluating a Published Report

The study described in the report is a randomizedcomparative experiment. Describe the treatment, the treatment group, and the control group.

The treatment is bathing in Epsom salt. The treatment group consists of the fifty subjects whobathe in the Epsom salt, and the control group consists of the fifty subjects who did not.




The study described in the report is a randomizedcomparative experiment. Describe the treatment, the treatment group, and the control group.

The treatment is using the old and new websites to make purchases. The treatment group consists of users of the website using the new website to make purchases. The control group consists of users of the website using the old website to make purchases



Explain whether the research topic is best addressed through an experiment or an observational study. Then explain how you would set up the experiment or the observational study.

Example 3: Designing an Experiment or Observational Study

The treatment may affect health, so it is not ethical to assign individuals to a treatment group. Perform an observational study. Randomly choose one group ofpeople who already use tanning beds at least twice a month and another group which does not. Monitor the incidence of skin diseases in both groups.




1000 mg of vitamin is not known to have any negative effects, so conduct an experiment. Randomly choose one group of people to take the supplements, randomly choose another group ofpeople to not take the supplements, and monitor the cholesterol levels in both groups.

Explain whether the research topic is best addressed through an experiment or an observational study. Then explain how you would set up the experiment or the observational study.



Example 4: Evaluating Data Collection Methods

Classify each method as a survey, an experiment, or observational study, and explain which would be most reliable.

Method A: Method B: Method C:

Choose 50 people who have at least one serving of soy a day and 50 who don’t, and check their cholesterol levels.

Randomly choose 100 people. Ask how many servings of soy they have a week, and ask if their cholesterol levels are high.

Randomly choose 50 people to eat at least one serving of soy a day, and 50 people not to, and monitor their cholesterol levels.



In Method A, the members of the study are self-selected. They may have a healthy diet in general. In Method B, the results are self-reported, so they may not be accurate. Method C is most reliable.

Continued Example 4: Evaluating Data Collection Methods

Method A: observational study Method B: survey Method C: experiment



Classify each method as a survey, an experiment, or an observational study, and explain which would be most reliable.





Method B is least reliable, because there is no basis for comparison. Method C has a comparison group, but the members are self-selected, which could lead to bias. In method A, the members of each group are randomly selected, so method A is the most reliable.

Method A: experiment Method B: survey Method C: observational study



Lesson Quiz: Part 1

A researcher wants to study the effects of a vitamin supplement on insomnia. Fifty people with insomnia volunteer for the study.

1. All of the volunteers are given a vitamin supplement daily and the amount of sleep they get ismonitored for a month. Is the situation an experiment or an observational study?

experiment



Lesson Quiz: Part 2

2. Which method would be more reliable, an experiment or an observational study? Explain.

An experiment would be more reliable because the volunteers may not already be taking vitamin supplements.



3. Describe how the study could be made into a randomized controlled experiment. In your answer, identify the treatment, the treatment group, and the control group.

Lesson Quiz: Part 3

Randomly select 25 of the volunteers and give them the supplement. Do not give the other 25 thesupplement. Monitor the amount of sleep that bothgroups get. The treatment is the supplement. The treatment group is the 25 people given the supplement. The control group is the 25 people notgiven the supplement.

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Holt McDougal Algebra 2 Surveys, Experiments, and Observational studies Holt Algebra 2 Warm Up Warm Up Lesson Presentation Lesson Presentation Lesson Quiz