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Surveys, Experiments, and Observational Studies

Surveys, Experiments, and Observational Studies. This information begins on page 23 of the textbook that you may get by the end of the week. Placebo Addiction. My brother is addicted to placebo. He’d quit but it wouldn’t matter. Experiment vs. Observational Study.

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Surveys, Experiments, and Observational Studies

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  1. Surveys, Experiments, andObservational Studies This information begins on page 23 of the textbook that you may get by the end of the week.

  2. Placebo Addiction • My brother is addicted to placebo. • He’d quit but it wouldn’t matter.

  3. Experiment vs. Observational Study • An experiment imposes a treatment on individuals to collect data on their response to the treatment. • An observational study observes individuals and measures variables without controlling the individuals or their environment in any way.

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

  5. Experimental or Observational • 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. • The employee applies a treatment (painting benches with latex paint) to some of the individuals (benches). The situation is an experiment.

  6. Experimental or Observational • 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.

  7. Controlled Experiment • 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. Treatment Group Controlled Experiment Control Group

  8. Evaluating a Published Report Milk Fights Cavities • At Ashland Middle School, fifty randomly chosen students were given milk at lunch every day for a year, and fifty other randomly chosen students were given other beverages. • At the end of the year, students in the “milk” group had 15% fewer cavities than students in the other group. Treatment: • Milk everyday at lunch Treatment Group: • 50 randomly chosen students Control: • Another 50 randomly chosen students

  9. Randomized Comparative Experiment • A randomized comparative experiment should be used to gather data whenever feasible because this type of study makes it possible to draw valid cause-and effect conclusions. • Such experiments are also reliable. That is, they can be repeated and can be expected to produce similar results each time.

  10. Experiment or Observational • What is the best way to answer the question: Does listening to an MP3 player with earphones for more than one hour per day affect a person’s hearing? • Could the treatment harm a participant? Yes • Due to ethical considerations you must use an Observational Study

  11. Experiment or Observational • What is the best way to answer the question: 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? • Could the treatment harm a participant? Nope • So conduct a randomized comparative experiment.

  12. What is the difference in an Observational Study and a Survey? • Surveys are not comparative • Surveys draw data from only one group • So Surveys cannot make conclusions about cause and effect • It is possible to give the same survey to two or more groups and compare the results – but that is a type of observational study!

  13. Survey, Experiment, or Observational • 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. • Method A • Choose 50 people at random. Ask which cold medicines they have taken in the past, and how effective they were. • This method is a survey.

  14. Survey, Experiment, or Observational • 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. • Method B • Monitor 50 people with colds, and measure the length of the symptoms for the individuals who choose to take each type of medicine. • This is an observational study.

  15. Survey, Experiment, or Observational • 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. • Method C • 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. • This method is a comparative experiment.

  16. Then explain which method would be most reliable • Method A is least reliable, because there is no basis for comparison. • Method B has a comparison group, but the members are self-selected, which could lead to bias. • In method C, the members of each group are randomly selected, which makes the two groups theoretically similar except for the variable, the different medicines. This method is most reliable.

  17. Homework 1-3 • Page 27 #1 – 33

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