Slide Slide 1 Copyright © 2007 Pearson Education, Inc Publishing as Pearson Addison-Wesley. Created by Tom Wegleitner, Centreville, Virginia Edited by Olga Pilipets, San Diego, California Design of Experiments

Slide Slide 2 Copyright © 2007 Pearson Education, Inc Publishing as Pearson Addison-Wesley. Key Concepts  Sample data must be collected in an appropriate way, such as through a process of random selection.  If sample data are not collected in an appropriate way, the data may be so completely useless that no amount of statistical torturing can salvage them.

Slide Slide 3 observing and measuring specific characteristics of objects without modifying them in any way. Example: Gallop poll ( observing through interviews) Copyright © 2007 Pearson Education, Inc Publishing as Pearson Addison-Wesley.

Slide Slide 4  In 1855 John Snow discovered that cholera is a waterborne infectious disease. Snow was a physician in London.  Some 20 years before Koch and Pasteur laid the foundations of modern microbiology  By observing the course of the disease, he concluded that cholera was caused by a living organism, which entered the body with water or food, multiplied in the body, and made the body expel water containing copies of the organism. Copyright © 2007 Pearson Education, Inc Publishing as Pearson Addison-Wesley.

Slide Slide 5  Snow explained the lag between infection and disease—a matter of hours or days—as the time needed for the infectious agent to multiply in the body of the victim (poisons work instantly)  cholera spread along the tracks of human commerce.  Furthermore, when a ship entered a port where cholera was prevalent, sailors contracted the disease only when they came into contact with residents of the port. These facts were easily explained if cholera was an infectious disease, Copyright © 2007 Pearson Education, Inc Publishing as Pearson Addison-Wesley.

Slide Slide 6  apply some treatment and then observe its effects on the subjects  Example: In the experiment designed to test the Salk vaccine, 200,000 children were given the actual Salk vaccine and 200,000 other children were given a placebo. Copyright © 2007 Pearson Education, Inc Publishing as Pearson Addison-Wesley.

Slide Slide 7  Cross sectional study data are observed, measured, and collected at one point in time  Retrospective (or case control) study data are collected from the past by going back in time  Prospective (or longitudinal or cohort) study data are collected in the future from groups (called cohorts) sharing common factors Copyright © 2007 Pearson Education, Inc Publishing as Pearson Addison-Wesley.

Slide Slide 8 Copyright © 2007 Pearson Education, Inc Publishing as Pearson Addison-Wesley. obtain that sample using an appropriate method, such as one based on randomness Replication and Sample Size  Sample Size use a sample size that is large enough to see the true nature of any effects

Slide Slide 9 Copyright © 2007 Pearson Education, Inc Publishing as Pearson Addison-Wesley.  Random Sample members of the population are selected in such a way that each individual member has an equal chance of being selected Definitions  Simple Random Sample (of size n ) subjects selected in such a way that every possible sample of the same size n has the same chance of being chosen

Slide Slide 10 Copyright © 2007 Pearson Education, Inc Publishing as Pearson Addison-Wesley. Random Sampling selection so that each individual member has an equal chance of being selected

Slide Slide 11 Copyright © 2007 Pearson Education, Inc Publishing as Pearson Addison-Wesley. Systematic Sampling Select some starting point and then select every k th element in the population

Slide Slide 12 Copyright © 2007 Pearson Education, Inc Publishing as Pearson Addison-Wesley. Convenience Sampling use results that are easy to get

Slide Slide 13 Copyright © 2007 Pearson Education, Inc Publishing as Pearson Addison-Wesley. Stratified Sampling subdivide the population into at least two different subgroups that share the same characteristics, then draw a sample from each subgroup (or stratum)

Slide Slide 14 Copyright © 2007 Pearson Education, Inc Publishing as Pearson Addison-Wesley. Cluster Sampling divide the population into sections (or clusters); randomly select some of those clusters; choose all members from selected clusters

Slide Slide 15  Random  Systematic  Convenience  Stratified  Cluster Copyright © 2007 Pearson Education, Inc Publishing as Pearson Addison-Wesley. Methods of Sampling - Summary

Slide Slide 16  Sampling error the difference between a sample result and the true population result; such an error results from chance sample fluctuations  Nonsampling error sample data incorrectly collected, recorded, or analyzed (such as by selecting a biased sample, using a defective instrument, or copying the data incorrectly) Copyright © 2007 Pearson Education, Inc Publishing as Pearson Addison-Wesley. Definitions

Slide Slide 17 Copyright © 2007 Pearson Education, Inc Publishing as Pearson Addison-Wesley. Recap In this section we have looked at:  Types of studies and experiments  Randomization  Types of sampling  Sampling errors

Slide Slide 18 #8 p. 31 Cruise ship passengers are given magnetic bracelets, which they agree to wear in an attempt to eliminate or diminish the effects of motion sickness. Copyright © 2007 Pearson Education, Inc Publishing as Pearson Addison-Wesley.

Slide Slide 19 #10 p.31 A researcher from Johns Hopkins University obtains data about the effects of alcohol on driving by examining car crash reports from the past five years. retrospective Copyright © 2007 Pearson Education, Inc Publishing as Pearson Addison-Wesley.

Slide Slide 20 #12 p.31 An economist collects income data by selecting and interviewing subjects now, then going back in time to see if they had the wisdom to take a statistics course between the years of 1980 and retrospective Copyright © 2007 Pearson Education, Inc Publishing as Pearson Addison-Wesley.

Slide Slide 21 #22 p.32 A market researcher has partitioned all California residents into categories of unemployed, employed full time and employed part time. She is surveying 50 people from each category. Stratified Copyright © 2007 Pearson Education, Inc Publishing as Pearson Addison-Wesley.

Slide Slide 22 #16 p.32 An engineering student measures the strength of fingers used to push buttons by testing family members. Convenience Copyright © 2007 Pearson Education, Inc Publishing as Pearson Addison-Wesley.

Slide Slide 23 #28 p.33 A researcher for the Orange County Department of Motor Vehicles plans to test a new online driver registration system by using a sample consisting of 20 randomly selected men and 20 randomly selected women. (Orange County has an equal number of male and female drivers). Does this sampling plan result in a random sample? A simple random sample? Yes, no. All drivers have the same chance of being selected, but some samples (such as those with 21 men and 19 women) have no chance of being chosen. Copyright © 2007 Pearson Education, Inc Publishing as Pearson Addison-Wesley.