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Surveys, Experiments, and Observational Studies: Commonalities and Differences

Learn about the similarities and differences between surveys, experiments, and observational studies in data collection, variables, and study design.

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Surveys, Experiments, and Observational Studies: Commonalities and Differences

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  1. Essential Questions • How do I focus on the commonalities and differences between surveys, experiments, and observational studies?

  2. 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. Individualsare 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.

  3. 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.

  4. 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.

  5. Example 1: Identifying Experiments and Observational Studies Explain whether each situation is an experiment or an observational study. 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.

  6. Example 1: Identifying Experiments and Observational Studies Explain whether each situation is an experiment or an observational study. 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

  7. 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.

  8. 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

  9. Example 3: Designing an Experiment or Observational Study 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. 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.

  10. Example 3 b 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. 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.

  11. Example 4: Evaluating Data Collection Methods Classify each method as a survey, an experiment, or observational study, and explain which would be most reliable. Observational Survey Experiment Self-selected Self-reported Most reliable

  12. Example 4 b Classify each method as a survey, an experiment, or an observational study, and explain which would be most reliable. Experiment Survey Observational Most reliable Self-reported Self-selected

  13. Lesson 1.3 Practice A/B

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