2. Holt McDougal Algebra 2 Surveys, Experiments, and Observational studies How do I focus on the commonalities and differences between surveys, experiments, and observational studies?

3. Holt McDougal Algebra 2 Surveys, Experiments, and Observational studies 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.

4. Holt McDougal Algebra 2 Surveys, Experiments, and Observational studies

5. Holt McDougal Algebra 2 Surveys, Experiments, and Observational studies 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.

6. Holt McDougal Algebra 2 Surveys, Experiments, and Observational studies 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.

7. Holt McDougal Algebra 2 Surveys, Experiments, and Observational studies 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.

8. Holt McDougal Algebra 2 Surveys, Experiments, and Observational studies C. 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. It is an observational study because an observation is being conducted without controlling the environment in any way Explain whether each situation is an experiment or an observational study. Example 1: Identifying Experiments and Observational Studies

9. Holt McDougal Algebra 2 Surveys, Experiments, and Observational studies Example 2: Evaluating a Published Report The study described in the report is a randomized comparative 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 who bathe in the Epsom salt. The control group consists of the fifty subjects who did not.

10. Holt McDougal Algebra 2 Surveys, Experiments, and Observational studies Example 2 b The study described in the report is a randomized comparative 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

11. Holt McDougal Algebra 2 Surveys, Experiments, and Observational studies 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 of people 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.

12. Holt McDougal Algebra 2 Surveys, Experiments, and Observational studies Example 3 b 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 of people 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.

13. Holt McDougal Algebra 2 Surveys, Experiments, and Observational studies 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. ObservationalSurveyExperiment Self-selectedSelf-reportedMost reliable

14. Holt McDougal Algebra 2 Surveys, Experiments, and Observational studies Classify each method as a survey, an experiment, or an observational study, and explain which would be most reliable. Example 4 b ExperimentSurveyObservational Self-selectedSelf-reportedMost reliable

15. Holt McDougal Algebra 2 Surveys, Experiments, and Observational studies Lesson 1.3 Practice A/B