SS - Observational vs Experimental Lesson
Observational vs Experimental Lesson
Adapted from Course materials (III.A Student Activity Sheet 1, 4, & 5) for AMDM developed under the leadership of the Charles A. Dana Center, in collaboration with the Texas Association of Supervisors of Mathematics and with funding from Greater Texas Foundation.
Statistical investigations are used every day for a variety of reasons. Statistical studies use a combination of mathematical and scientific techniques to answer questions about human behavior, the effectiveness of medical treatments, the safety and reliability of machinery and products, and so on.
Consider the following examples of two different types of statistical investigations.
Observational Study
An observational study is research in which data is collected about some characteristic(s) of the population. The data can be collected by observation or by a survey or interview or by other means. The following approaches are examples of an observational study:
Radio rating services sometimes collect data on listenership by asking participants to record the date, time, and station each time they listen to the radio. Other rating services distribute monitoring devices that automatically record this information anytime the participant has the radio turned on. Still, others call participants and ask them about their listening habits. The data are then compiled so that advertisers know which stations are the most popular at specific times during the day.
A group of middle school students want to know if they can use height to predict age. They take a random sample of 50 people at their school, both students and teachers, and record each individual's height and age. This is an observational study. The students want to use height to predict age so the explanatory variable is height and the response variable is age.1
Experimental Study
In an experimental study, the researcher separates the participants into one or more groups and applies some sort of treatment. After treatment, the variable of interest is measured and the results are compared. A group of participants that the treatment group is being compared to is called the control group. Researchers are often concerned that participants in a study show improvement simply because they are in the study and not because they are receiving an effective treatment. This is called the placebo effect.
A 17-year-old student designed a science fair project with 72 mice randomly assigned to three groups: hard rock music, Mozart, and no music at all (called a control group). The mice in the first two groups were exposed to music 10 hours a day. Three times a week, all of the groups were timed as they ran through a maze. An analysis of results showed that the 24 mice in the no-music group averaged about a 5-minute improvement in their maze completion time, while the Mozart mice improved 8.5 minutes. The hard rock mice actually got slower—an average of four times slower! Another interesting fact: The student had to start his experiment over because all the hard-rock mice killed each other. None of the classical mice did that. Wertz, M. 1998.
What are the treatment (explanatory variable) and the variable of interest (response variable) in this case? The treatment is the type of music. The variable is interest is the maze running time.
Summary
| Observational Study | Designed Experiment |
|---|---|
| A study where the researcher(s) observes individuals and records information. No treatment is imposed. | A study where the researcher(s) intentionally imposes treatments on individuals and measures their responses. |
| Reports an association (not cause and effect). | Reports a cause and effect relationship. |
| Example: A survey is an example of how data can be collected for an observational study. | Example: Testing a new medication; one group receives a placebo while the other receives the actual medication. |
| May or may not use random sample sets. | Randomization of a sample group. |
| May or may not generalize a population. | Generalizes to a population. |
| Less expensive. | More expensive. |
Observational vs Experimental Lesson Self Assessment
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