Chapter 11.1

Measures of Dispersion and

Types of Studies

1) Work out the average (mean value) of your set of numbers

2) Work out the difference between each number and the mean

3) Square the differences4) Add up the square of all the differences5) Divide this by the number of numbers in your

set (this is called the variance)6) Take the square root of the variance and

you've got the standard deviation

The last test scores for a small class were 45, 70, 75, 85, and 100.Find the standard deviation for the data.

Race B

4, 7, 8, 8, 9, 10, 10, 12, 13

Find the standard deviation for the data.

 

Types of Studies

Experimental Study Perform an experiment by applying a treatment to part of a population and observing responses. Usually there is a control group.

Example: A shampoo company wants to test a new and improved formula. Subjects are randomly assigned to two groups. One group gets the new formula, while the other group gets the original formula. The original formula group is the control group.

Types of Studies

Observational Study Observe individuals and measure variables of interest but do not attempt to influence the responses. NO treatment is applied.

Example: A study looked a cell phone use and the risk of brain cancer. They matched each brain cancer patient with a person of the same age, gender, ethnicity, etc. who did not have brain cancer, and then asked each group about their cell phone use.

Sample Survey

A sample survey is a type of observational study. Surveys are used to collect data on a target population.

Example: This question is best addressed with a sample survey: “Are people generally satisfied with how things are going in the country right now?”