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1.5

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    1.5 1.5 Presentation Transcript

    • Section 1.5 Chapter 1
    • 1.5 Design of Experiments
      • Observational Study
      • We observe and measure, but make no attempt to modify the subjects or outcome!
      • Cross-sectional: Data are collected at one point in time.
      • Retrospective: Data are collected from the past by using records, interviews, so on.
      • Prospective: Data are collected in the future from groups sharing common factors (cohorts)
    • 1.5 Design of Experiments
      • Experiment
      • We apply some treatment to modify the subjects or outcome.
      • Key elements of an experimental design:
      • Control the effects of variables.
        • Control the placebo effect (where someone thinks he/she is getting better if he/she knows if they are taking a new medication instead of just a placebo and vice versa) by blinding.
        • A double blind experiment is really what you want because in this scenario neither the patient nor the observer knows if the patient is taking a new medication or the placebo.
        • Put subjects into similar blocks so that variables are controlled
        • Confounding occurs if you can’t tell which variable really affected the outcome.
      • Replicate the experiment over and over with more subjects.
      • Randomize . Choose your sample very well.
    • 1.5 Observation or Experiment Examples Pg. 34 #6, 8
      • Determine whether it is an observational study or an experiment.
      • A Gallup poll surveyed 1018 adults by telephone, and 22% of them reported that they smoked cigarettes within the past week.
      • A study of the effectiveness of Echinacea involved 707 cases of upper respiratory tract infections. Children with 337 of the infections were given Echinacea, and children with 370 of the infections were given placebos.
      Observational study . No treatment was applied to the subjects. Experiment . A treatment in the form of Echinacea was given to some of the subjects.
    • 1.5 Cross-Sectional, Retrospective, or Prospective
      • Identify the type of observational study (cross-sectional, retrospective, or prospective)
      • 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.
      • Physicians at Mount Sinai Medical Center plan to study emergency personnel who worked at the site of the terrorist attacks in New York City on 9/11/01. They plan to study these workers from now until several years into the future.
      Retrospective. Prospective
    • 1.5 Types of Samples
      • Random Sample
        • Each individual has an equal chance of being selected
        • Simple random sample (SRS)
          • Every possible sample of size n has an equal chance of being selected
      • Systematic
        • Select every 10 th person, for example.
      • Convenience
        • Choose subjects that are easily available.
      • Stratified
        • Divide the population into subgroups and then draw a sample from each subgroup.
      • Cluster
        • Divide the population into clusters. Randomly select some of the clusters , then choose all the members from those selected clusters.
    • 1.5 Types of Sampling Used Examples Pg. 35 #10, 12
      • Identify which of these types of sampling is used: random, systematic, convenience, stratified, or cluster.
      • A study of the effectiveness of Echinacea involved upper respiratory tract infections. One group of infections was treated with Echinacea and another group was treated with placebos. The two groups were determined by a process of random assignment.
      • The author was an observer at a sobriety checkpoint at which every fifth driver was stopped and interviewed.
      Random Systematic
    • 1.5 Types of Sampling Used Examples Pg. 35 #14, 16
      • Identify which of these types of sampling is used: random, systematic, convenience, stratified, or cluster.
      • The U.S. Department of Corrections collects data about returning prisoners by randomly selecting five federal prisons and surveying all of the prisoners in each of the prisons.
      • The author surveyed all of his students to obtain sample data consisting of the number of credit cards students possess.
      Cluster because we grouped then chose all Convenience
    • 1.5 Types of Sampling Used Examples Pg. 35 #18, 20
      • Identify which of these types of sampling is used: random, systematic, convenience, stratified, or cluster.
      • In a study of college programs, 820 students are randomly selected from those majoring in communications, 1463 students are randomly selected from those majoring in business, and 760 students are randomly selected from those majoring in history.
      • In a Gallup poll, 1003 adults were called after their telephone numbers were randomly generated by a computer, and 20% of them said that they get news on the Internet every day.
      Stratified because we grouped then chose a sample Random
    • 1.5 Simple Random Samples Examples Pg. 36 #22
      • A quality control engineer selects every 10,000 th M&M plain candy that is produced. Does this sampling result in a random sample? Simple Random Sample?
      No and No. It is not a random sample because the second, third, fourth etc. M&M’s have no chance of being selected. In a simple random sample, each individual must have an equal chance of selection.
    • 1.5 Simple Random Samples Examples Pg. 36 #24
      • In order to test for a gender gap in the way that citizens view the current President, the Tomkins Company polls exactly 500 men and 500 women randomly selected from adults in the United States. Assume the numbers of adult men and women are the same. Does this sampling result in a random sample? Simple Random Sample?
      Yes, no. All adults have the same chance of being chosen, but some samples (such as a sample with 600 men and 400 women) have no chance of being selected since our selection process requires exactly 500 men and 500 women.